There are only a few improvements that seem to be needed to appease most people on here:
DMR needs to be tweaked so it is not the most powerful gun in the game at all ranges. If it was fixed so it was not good close range then it would suddenly be that much more balanced of a game. We would have the four different ranged guns then. LR is already balance this way, its 3 round burst is weaker than the other weapons at close range. There are ways around this but it takes a lot more skill than any other loadoat weapon to pull them off and win a close skirmish. So either tweak DMR’s dominance or replace completely with the already balanced Lightrifle.
Solid ranking system to separate the different skill levels.
Boltshot range is too great, needs a slight tweaking.
Need an option for a normal FFA and a Slayer without ordnance (dont remove current options, they are fun we could just use a more balanced option for competitive play)
A working file share and 343 taking map designs from the community to use in MM. The community is good at balancing maps that are kind of boring but work better for competitive play.
If we had these improvements halo would be a very balanced game. Still wouldnt be perfect, but the constant griping would go down considerably. All These things are fixable via TU. DMR problem maybe not such a simple fix.