The game has always distributed gear on a group result basis, not on individual contribution. This has
nothing to do with TF. You achieve a result with a group, you get rewarded according to the outcome, not the 'effort' which would be undecidable anyways.
Personal loot, while you can have questions whether it should be forced on e.g. guild runs, is definitely the right way to go for PUGs.
Loot has always been RNG. You could farm for your trinket, best stat ring or set-piece for an entire tier without ever having it drop for you, while the derp friend got it on his first carry through.
From a scientific point of view, variable reward reinforcement beats fixed reward reinforcement by miles in term of engagement and retention. This is just a
fact, backed up by many reproduced and detailed studies, regardless of your or mine opinion or preference. It is so scarily efficient that often we have to limit it's use through regulation to protect those captivated.
You can argue about its ethics, and morals, but if you are going to blame TF, or reward RNG in general, for reduced engagement or retention, you better come with some realy convincing detailed
causal research and analysis.
Extraordinary claims require extraordinary evidence.
And lastly: if you are that interested in the topic, learn about the specifics of the W/T system. No, variable reward does not mean random reward. While the specifics of the model used are not published by Blizzard, it is not that hard to re-engineer a fairly close approximation based on the analysis of the reward stream data of your guild. Then you might learn that the model is actually very nicely tuned to
preserve the difficulty stratifications in the game.