I've read this entire thread, and I see where both sides are coming from. Despite the fact that the conversation has devolved at points to name-calling and accusations of low skill, I'll try to introduce a more balanced line of thinking here.
Reach was the second online multiplayer game that I played using Xbox Live. I enjoyed it more than Halo 4 and Halo 3; I found it to be more fun. I would say that most of my time spent playing Reach, I didn't really know the difference between TU and Vanilla, besides the Armor Lock nerf. I have Perfection medals in both Vanilla and TU game modes; specifically Team Slayer, BTB, one Perfection in Doubles and possibly one in a match of Super Slayer. I especially enjoyed Rumble Pit and Multi-team, and it saddens me that those playlists are ghost towns at this stage in OG Reach's lifespan. I also liked Team Slayer and Invasion.
When switching between BTB and Team Slayer, for instance, I can say with confidence that I never particularly noticed the difference between 100% and 85% bloom until recently. And, while I may have noticed Melee bleed through in Rumble Pit, I wasn't bothered by it, at least that I can remember.
I don't believe the emptiness of most of the TU modes is due to the way the game plays, but rather the nature of the playlists and the unfortunate naming of Super Slayer. Super Slayer is a weird name, and it's not immediately clear what kind of playlist it is. Why take a chance on that, when you can go to a playlist with a trusted name like Team Slayer? Sure, Super Slayer has a description that lets you know it uses the Title Update, but I suspect (yet, admittedly, cannot prove) that a large portion of Reach's returning player base also didn't really know what "Title Updated" actually meant, much like myself. And there are players who don't bother to read the descriptions of playlists. "Super Slayer" immediately reads like a playlist with unfamiliar game modes, which means that fun isn't a guarantee (not that there would necessarily be guaranteed fun in Team Slayer, but at least Team Slayer is a no-brainer).
Team Objective is dead because most players would rather play various kinds of Slayer modes.
Rumble Pit is dead because FFA playlists are usually among the least populated lists in any given Halo game; players would probably rather have the safety of a team than fend for themselves most of the time.
I guess Multi-team and Doubles are dead because they're too niche for a game with a small playerbase.
BTB has kept a consistent population at certain times of day because it's easily understandable and not really a risk (unless you get an awful Forge map with Single Bomb, lol).
With all that said, I offer my thoughts on TU:
I'll start by saying that, over the last year, the times that I went back to play OG Reach I usually picked Team Slayer because it's straightforward and always populated, much like the TDM playlist in any given CoD. I found that 100% Bloom was incredibly infuriating because of the sheer amount of randomness that it creates. Pacing your shots at any range takes a long time, giving the enemy player plenty of opportunity to spam back or run for cover. I believe that rewarding players who spam for that one lucky shot at mid-to-close range with the DMR (or Magnum) and therefore punishing players who take the time to pace their shots... is inherently bad game design.
I found myself becoming so frustrated with the inconsistency of gunplay that I preferred BTB for gameplay style, except BTB is full of quitters and awful map + mode combinations.
Now, having played plenty of AR starts FFA in MCC, I find the Magnum to oh-so-rewarding. It's very satisfying to pace one's shots perfectly, beating an enemy player who is spamming their shots, be it with their own Magnum or a spray-and-pray Assault Rifle. The DMR in BTB I don't find to be problematic, mostly because the maps have a lot of cover and there are plenty of ways to escape situations, such as Sprint or Jetpack. With that said, I'm not opposed to AR starts in BTB.
tl;dr, I prefer 85% Bloom because it rewards pacing your shots much more than 100% Bloom ever has.
Now, as for shot and melee bleed through, I sympathize with the people who don't like the unpredictability that it creates in TU Reach. Knowing when you are one-shot is a consistent kind of indicator in Vanilla modes, and it means you can base your play style around that. It's sometimes frustrating to not know if your remaining shields are strong enough for you to endure another headshot. Likewise, Melee bleedthrough can create a game of frantic button pressing in CQC, especially with the healthy melee lunge and magnetism. It can create some unsatisfying trades.
However, it's also frustrating to know that if someone hits you first in Vanilla, and they have even a sliver of their shields left, they will win that fight--unless you have a power weapon--by simply hitting you again. Halo's multiplayer has usually been distinct from other shooters because of the amount of tactical options it allows in many situations, as opposed to giving the victory to whomever hits first.
tl;dr, I have no strong opinion on bleedthrough either way. I think Melee damage could stand to be reduced slightly in TU, but I don't necessarily prefer Vanilla settings.