The following does not come from the perspective of an ACR convert because I'm not, yet. I think the concept is very sound, but I continue to wait for the new rifle's growing pains to dissipate and for the full measure of its promise (read: caliber changes) to be realized. So that's the perspective from which I make the following comments:
It seems from your account that the ACR in no way failed to perform as advertised. Even so, with respect, I would be shocked if you did not miss your old platform. Allow me to borrow an analogy from your urban brethren: You've been walking the beat with your original partner for God knows how many years. Now he has retired to make way for this rookie. The new kid is a good cop, maybe even a better cop than your old partner was. He comes from a newer and more sophisticated era, the product of many lessons learned the hard way. (How reluctant would you be to admit that, if we were talking about people rather than rifles?) Still, it is absolutely unreasonable to expect even a very talented new partner to work with you
as well as did the old in a crisis, unless you have personally drilled the hell out of that rookie for every crisis imaginable. There are simply too many years of induced telepathy between you and your old partner which can not be immediately replaced. So even if the ACR dramatically outperformed your AR-15 in the day's events, I would still expect you to feel some nostalgia and longing for your old partner during and after.
I ask you, therefore, to take pains to consider the situation in as objective a light as possible. Think back to when the AR-15 was new to you? Were there acclimitization difficulties? Were there personal disagreements you had to work out on the job which did not reveal themselves in standard qual-training? I would be willing to bet there were a few, owing to nothing more than the Stoner-pattern's rather silly manual of arms. ("All right, I've got the rifle in my right hand and the perp in my left and my flashlight in my mouth... Oh, shit, my bolt is still locked back. Now what am I supposed to do?") Consider how you overcame these, and how long it took you to overcome them, and then decide, with as much grim objectivity as you can muster, whether or not it is too late in your career to be breaking in a new partner.
Also, as you decide whether or not the ACR is worth that effort, consider how much effort, on and off the job, is actually required. You've already stated that one of your problems came from loving the operating method of the ACR perhaps a little too much. That's a better starting place than the alternative. You mentioned that you've qual'd with the gun, but have you trained with it? If police work is anything like military work, the basic education required to "qualify" is pretty damn basic. It usually amounts to accuracy vice time in a draw and shoot on a square range against a frontal silhouette. This does not constitute training. If you want to shorten the time it takes for you to mind-meld with your new partner, then you might avail yourself of more rigorous and regular scenario-based training (at the expense of personal time and money, of course, because that's how it always goes). Even a basic Blackwater (now U. S. Training Center), Magpul D, or similar company's LEO clinic would include scenarios like the one you describe--at least sufficiently similar as to have presented the same problems. And even if you can't get to one of those schools, you can do your own scenario brainstorming with your comrades at work. Consider a product such as Chamber Check
to safely practice managing the gun (the actual gun, rather than a training nongun) while performing other tasks.
Again, it is entirely possible that this is more than you care or can afford to invest in your new weapon system, but I offer it for your consideration, because again, it seems that the ACR worked quite well for you that night. Let me now address the three specific points in your anecdote:
The battery: As you said, irrelevant except inasmuch as it represents an incidental plus point for the gun's storage compartment. I'm sure you would have had batteries on your person regardless.
The bolt operation: Some clarification may be required here. As I understand the ACR's operation (specifically its non-reciprocating charging handle), the bolt should cycle when you cycle the handle, but the handle should not cycle when your rounds cycle the bolt. Therefore, after the last round is fired, the bolt should lock open, but the handle should still be in its forward position. This is normal operation. Upon loading a fresh magazine, you can release the bolt either by stroking the handle (as long as you are disciplined about not riding it forward, just as with a pistol) or by depressing the release. I can sympathize with your reason for operating it oddly; I too tend to love on my guns in my spare time, play with them. It is our responsibility to have the discipline to love them according to the manual of arms just as we train according to the manual of arms. Play like you practice, and practice like you work. Be consistent. Which is not to say that you can't train for variety. If you love the bolt release at home, train to use it in the field as well. At least make sure that whichever path your neurons take will result in proper operation of the rifle. Make sure that by handle or by button, that bolt will slam all the way into battery 1000 times out of 1000. I imagine that in scenario training, you will find a lot more use for the bolt release method than the power-stroke method, which ties up your "reaction" hand that much longer when it could be doing something else, like signaling a teammate or controlling a suspect.
The weight and forward CG: This is a legitimate concern. Setting aside the usual "Just grow some biceps, pansy!" (for we are not all SWAT/SPECOPS with nothing better to do than lift and eat), this problem would be simply remedied with and aftermarket of barrels. Again, this is the principle reason I have not yet committed to purchase this rifle, as a barrel aftermarket is supposed to be one of its principle selling points. I have no doubt that if/when this aftermarket opens, a slim-profile 12" barrel will more than alleviate the weight and CG issue you encountered. In the meantime, I understand there are custom gunsmiths who can produce such barrels if you are willing to pay for them. And of course I will not entirely discount the thing about biceps either. Training to handle a heavy load is a simple matter. At least you're not the infantry guy stuck carrying a .308 battle rifle or a machine-gun.
I think that covers everything that occurred to me as I was reading your post. I must stress for a third time that this is not to say you should stick with the ACR. Only that some acclimitization is to be expected, and you must weigh the cost of the necessary training (in time and money, and really money is time) against the potential benefit. Imagine yourself fully melded with the ACR, able to take full advantage of the capabilities it provides, like a finely honed cyborg. That's the potential benefit. Everyone will weigh that equation and come up with a different answer.
--And that reminds me of my final thought: If you decide against, then I think relegating the ACR to home-defense purposes is the last thing you should do. The weapon on which your family
depends, in the dark of night when you are bleary and ill-rested and not expecting trouble and you do not
have the rest of your force to back you up, is the weapon with which you should be absolutely the most familiar and the most natural. The gun at your bedside should be the one that is most a part of you, because it is the one you will operate under the absolute least favorable conditions, psychologically and physiologically. Thus I advise, sir, that you pick one rifle and make it a part of you. And then get a silencer for it if you're really going to use it for home defense. A .223 in an enclosed corridor, with sleep-adapted eyes and ears, will rock your world, and may prevent you from hearing and interpreting auditory or visual cues amidst the screams of your children. Not something one desires to contemplate, but a necessity in the reality of such a situation.