I'm kinda happy that people left for BF3. Those guys weren't the ones interested in this game in long term anyway.
You're wrong about this. Folks can enjoy more than one style of gaming simultaneously. I stopped playing RO2 after playing only maybe a week or two, and am currently quite enjoying BF3 (well, when people recognize that you have to actually arm/disarm objectives in Rush mode...but I digress).
But I also played plenty of the RO UT2k4 mod, and played the HELL out of RO:Ost. Some of my fondest memories in gaming are playing Berezhina (in my opinion, the most perfectly designed combined arms map of the RO:Ost era). I loved playing the slow advance, the mad dash into an objective, praying you wouldn't get picked off by someone with a boltie, etc.
RO2, though, I've found to be....different. Not what I wanted. It tries too hard to borrow from the BF3/MW3 aspects of FPS gaming, while holding on to the RO:Ost elements, and ends up doing a disservice to both, in my opinion.
I'm very much against the high numbers of auto and semi-auto weapons on the maps, as well as the whole "avatar stat" improvement system. I accept these things in games like BF3, but I didn't want them in an RO game. I especially didn't want them the way RO seems to be doing it by literally making your avatar BETTER simply because you've played longer. It'd be one thing if you had "sidegrades" but the stat improvements are true "upgrades," which makes an already newbie-unfriendly game even more unfriendly. Frankly, I'd get rid of the whole unlock system except for cosmetic differences and meaningless baubles like "ranks" which don't confer anything on you except maybe a shiny symbol next to your name on the scoreboard or a new skin you can use.
I'm on the fence about other changes, such as the cover system (which seems cool as a concept, but also dodgy as executed), and the bandaging/bleed-out thing.
Really, though, the game just felt very much like a hybrid of two extremely distinct styles of gameplay, but didn't go far enough in either direction. I'm not sure if that can be changed. I'd hope that a robust SDK might result in community "fixes" for most of this stuff, but that also raises questions of what exactly RO:HOS brings to the party that you couldn't get from RO:Ost.
Regardless, I loved RO:Ost dearly. I'm thoroughly enjoying BF3 and enjoyed BFBC1 and BFBC2. So the notion of "F*** 'em. Let 'em leave. They were never SERIOUS RO players anyway", really isn't true. I left RO, but from my perspective, RO left me first. I'd happily return if I could get the kind of gameplay I'm looking for, but that's pretty much RO1 with maybe a few other additions to gameplay that tend towards more realistic/tactical gameplay, rather than towards the "fast shooter" approach that I get from BF3. If I want that, I'll just play BF3. If I come to RO, I want what, in my mind, is the RO experience.