I can see it without testing for it, and it has been in every game in at least one weapon. Every weapon had it in CE (except for the sniper rifle, shotty, and rocket launcher, aka same deal with Reach)
Bloom is a replacement for decreasing the fire rate of certain weapons. Halo 3's pistol and BR fire extremely slow because the shots are always on target, and bloom technically doesn't exist. If you get into a CQB you want to fire faster because your target is extremely 'large'. This is like saying Halo CE is not true to the essence of Halo because back in the day you could fire faster more inaccurate shots like how Reach just tells you how much accuracy you're losing. Including bloom and showing it balance out a lot of elements of the game (sure there are wildcards but the fundamental gameplay works). Maybe people left because Halo 3 was like Halo 2 and Reach was like neither, Halo 2 had one weapon with bloom and a few with spread, and Halo CE was never online making it hardly within anyones memory or concept of good Halo multiplayer a decade later.
MLG probably dropped it because it was otherworldly compared to Halo 2 and 3, same reason why people left.
Reach is actually a return to Halo CE more than any other game. There is an increase in bloom compared to how it was in CE but how many new ways are there to kill people?