That's fine, I don't have a problem with the third hit of a combo (or in general, a skill that does enough damage to interrupt, say over 150-170 potency before buffs). However, my point remains and your example doesn't necessarily address that (trying to interrupt with cast times, trying to meet that threshold within a single GCD). You can hold off your combo skills, but melee doesn't have that luxury, and the amount of abilities that do so are far and few inbetween (silences specifically). Like I mentioned before, a cast shouldn't be interrupted by a a sneeze, but it the threshold shouldn't be so high that a BLM can get casts off while a melee is wailing on him (and said BLM is standing still). That's what skills like equanimity and surecast are there for.
Those walls were not torn down because of Los, like the general consensus seems to deem it. Everyone who's been in feast has to admit the walls surrounding the adrenaline cramped the middle way too much. throw 16 players in there, and it was a cluster eff of name and hp bars.
As far as developer response was concerned, I definitely feel that the change was in relation to that, though most likely among other things too as you mentioned.
That's the point of a discussion like this to get inputs from both sides, but ok.
The problem with removing Ilvl sync is that it can start to get out of control with the numbers, especially if we take morale as is. It could be something like raise the player's level in relation of things like defense, mitigation and accuracy (you deal less damage to someone that's lower level than you). Or a straight % buff to attack, defense and healing. Ideally, you'd get the gear only as you need them (which is usually separated by rank tiers). If you were silver rank, you'd pair with other silver rank, but you're unable to wear gear that only gold or higher than buy, so on and so fourth.