Right, which is why I said I'd rather have a gentlemen's agreement not to play with flyers for most games. Its no fun to play against a flyer heavy list if you don't have any anti-air. Its no fun to play against a baneblade if it takes your entire army 4 turns to kill it which means you aren't killing his other stuff and he's wiping out numerous units a turn. Its no fun to play against a screamer star that's got a re-rollable invuln save using biomancy/divination combo.
Any time you've got a near invulnerable unit or chunk of units on the other side, its just not a fun game. So for casual games you come to an agreement about what you want to play. For tournaments you know what is allowed and plan accordingly.
I don't think the FOC changes are really a big deal, but I've never run into problems with not having enough slots. I mean, the best heavy slot for marines is also dedicated transport, so you can get more than you have points for in a sub 2000 point game.
Also, how are you getting those flyers in the rear several turns in a row without going into hover mode and then getting blasted out of the sky? Last I checked they didn't have any of those cheap tricks eldar or CSM use.
PS: The formation only changes one of the 3 flyers to BS 5, 2 of them are already BS 5. So it really is a minor benefit. Of course, the cheese thing to do, since its another detachment, is to say "this flyer detachment is an iron hands detachment" to get free FNP despite the rest of your army being whichever you prefer.