Well, EVERYONE uses ACR! At least when you prestige, you get a chance to get some experience with the other guns again. You're forced to!
FWIW, the first time I prestiged, I thought it was difficult but you'll find yourself doing just as good pretty quickly, and even getting better. The hardest part initially is getting used to other weapons again. I'm at level 40-something now on my second prestige. The first time, I felt like you. But this second time, I've been doing well right from the start even at the lowest levels, maybe because I knew what to expect. You won't get quite the same crazy number of kills because you don't have the same killstreak rewards right away, but you should find yourself doing well again pretty quickly.
For me, not having Ninja Pro is the biggest annoyance. I love the silent footsteps. I also miss Cold Blooded and the Stinger for taking out air support. Otherwise, it's really not so bad. You get ranked against lower players than when you're level 70, and as a result, you'll find yourself winning most of the close combat one on ones.
I stuck around level 70 on 1st prestige for quite a while. This time, once I get past level 70, I'm going to 3rd prestige right away. I like the AK47 (a lot!), but I have more fun leveling up from level 1.