Ideally it stays at a locked 60. But barring that I agree with your post. But in competition, once a player can realize an advantage that person will always use it. So that 20-30% could result in 20-30% better aiming, recognition that someone could be shooting at you etc. It's likely to add up as a large benefit over the long haul. Of course console is equal playing field so perhaps that point is moot, but I think we get each other.
Having played a lot of destiny PVP vs something like Titanfall on XBO, i much prefer TF. Even with it's imperfect frame update.
I don't think you can go from 60 fps looking 20-30% better to it having a similar impact in terms of gameplay . While the 30 fps moon doesn't look quite as nice in motion as the 60 fps moon, it still is perfectly targetable. Maybe you can say 60fps makes it 5% easier to target very fast moving targets, but even then things like the player's skill at tracking a fast moving target and their aiming sensitivity settings will be vastly more important at determining whether they hit said target rather than the framerate (though obviously if its not a solid 30 fps and fluctuates between 15/20-30 or so, then you're going to have issues).
I played significant amount of MP time in COD4, MW2 & Black Ops on 360/PS3 and while I enjoyed it, I still preferred Halo or BF3 in terms of gameplay/ gunplay (though not BFBC2 incidentally, they made a big improvement in gun handling from BFBC2 to BF3). And I think that's down mostly to the mechanics and pace of the games rather than the 60 vs 30 fps.
And judging by the huge success of 30 fps Destiny, vs ~60 Titanfall which fizzled out, I don't think any overwhelming preference for 60 fps gameplay in MP shooters is evident.
COD games are so popular because of their mechanics, they are much easier to pick up and play than something like Halo or BF, I know noobs who'll run around with an M60 in COD and rack up loads of kills but'll struggle to get a single kill in Halo (because you can't just get see a guy first, spray half your clip and kill them with the 4 bullets you landed). Ditto with BF, which takes at least 20 hours, just so you can be ranked in the middle of the post-match summary (I know, because it took me about that long to do exactly that in BF4 on PS4, despite spending 100+ hours playing BF3 on 360 - albeit with a 1+ year gap of not playing BF in between).
So I think 343i trying to replicate COD's success by matching them on framerate is silly. They tried to bring the mechanics more in line with COD's in Halo 4 and failed miserably, and even if H4 was 60 fps people would still prefer playing 30 fps Halo 3/Reach.
Other than mechanics, COD is also a gaming institution that is assured runaway success merely based on its past success and the network effects of the huge COD community and the fact that even non-core gamers and non-gamers are familiar with the franchise.
So all those things are going to be hard to trump, and saying framerate is the major reason why COD is so successful seems like specious reasoning to me.
