Funny how you take the tank as an example, when they actually are the exception in how we currently compete with loot. And that exception is absolutly unjustified. So is the possibility of you running as RDM and getting mached with two BLM, another RDM and a SMN in the same party and having to roll against 4 other players.
A loot distribution system being mostly impacted by what role/job people play makes no sense. Then the desynth/seals people will roll on freaking belts from the first boss and finish the raid to get their token. That's as much people who won't compete for your MCH's pants from the 3rd or 4th boss.
Well, if that DRG main wants healer gear, then yes, why would that player not get a chance at it? Besides, he can currently get in as a healer for that, so what's your point? Forcing him to play a specific job achieve nothing. Besides, as I said above, some jobs/roles can be in a better/worse position to get their loot with the current system. And that's ridiculous. Making it "unfair" equally for everyone is actually making it balanced. No matter if you like the new odds or not. Or maybe do you think that it's actually fair that a tank get his gear 100% secured, healers at 50% competition, and DPS ranging from 100% to 20% for absolutly no reason whatsoever? The current system is unfair. We can already roll on something for an alt-job while someone would've needed it for their main. The only difference is that we had to play as that job/role to get a roll on it. Your co-healer in your party might very well be a MNK main but decided to get in has a WHM to get the neat robe for glamour.
The new system simply removes the unfair odds of competition by making every job/role on the same page. As it should be. There's no reason why tanks don't have to compete for loot, while healers have 1 competitor and DPS can have up to 4.
It's not a "downside" to open competition for jobs/roles which had a easier time at getting loot than others for no apparent reason. At least, with greed only, everyone has the same odds for everything.
The only dowside is the seemingly lower (but equal for everyone) chances on average of getting something, which is why I suggested increasing the number of drops in each chest.