Yeah, I'd count the armor as a follower of sorts.
Does RL-3's accuracy improve as he levels up (I don't have BS yet)? Because I'm quite serious, I saw him get reduced to scrap by a Robobrain because it was hitting at a distance, and RL-3 wasn't. He was a great follower early on, but once I got up to about level 10 or 11, I was reloading right and left just to keep him with me. I was tempted to say forget it, scav him for scrap and flamer fuel, and press on alone. But the game got accidentally erased before I got to that point.
I find him very powerful as I level up, and I've not managed to lose him yet. At level 30 he feels like a floating tank (defeated a behemoth without dogmeat help), the noise he made when being smacked around sounded very unhealthy and he spun about about each time the behemoth hydrant clobbered him, but it sounded worse than it was and the old bot didnt take that much damage in the end. The main problem with his plasma gun I find is clipping scenary when the targets are above or below us, on level ground against an enemy that isn't running he seems quite accurate (not sure if this has improved as I leveled up though). He also has decent storage capacity (don't ask me where he sticks it.. I haven't worked that 1 out yet! ).
I find it fun having RL3 and the medic power armor at same time, sounds like I have a unit of squaddies by my side!