Nobody is against new features and variety in Halo. Those 3 specifically broke the Halo sandbox, however.
I'll go on loadouts first. Custom loadouts make sense for a side-show gametype, but not the entire game. When anyone can start with a Plasma Pistol or Shotgun-type-weapon on every map, you can't design the map around a specific playstyle since they don't have to pick the weapon off the map.
This also created problems in BTB, like since everyone can now start with a Plasma Pistol, vehicles are now super vulnerable since they can be EMPd by everyone off spawn.
Usually in a Halo game you'd fix this by tuning the gametype for each map or playlist. PP too OP on a map? Turns out people are abusing the shotty in Doubles? You can just delete the weapons off. But now that you let everyone choose them, you're stuck with them everywhere. Reach at least had the ability to remove loadouts that were OP or remove them entirely if they didn't work out. Halo 4 could have just used it to select your weapon skins, but they had to go HAM on it.
So Perks are introduced. Perks ruin the readability and consistency of the Halo sandbox. They counter the bad idea of the PP being available off spawn 24/7 by letting you choose a perk that cancels out the EMP effect. They counter everyone having a rocket launcher available for standing in one spot by adding a perk that lets you survive your vehicle being destroyed. They ruin the entire point of the shields/shot system by letting your shields last longer than other people's with no way to tell. Standard functionality like the Red X was removed and shifted over to being a perk, because who knows why. And guess what.. most of them were locked off unless you coughed up more money, meaning that people that had more money than you had more capability than you did.
And then they dug in even more by selling more perks down the road.
Ordnance broke the entire weapon sandbox. You could call heavy weapons to anywhere on the map, including the best spot to use them. If you started to win, you got to win even harder by having weapons delivered to you. There was no weapon loops anymore (having to retrieve a good weapon from the worst place to use it to the best place to use it) which meant map movement became irrelevant. Forging maps no longer mattered because your map was just a backdrop to 343's universal gametype. I could forge a great map where a sniper rifle was on an exposed bridge, didn't fucking matter because someone could just summon one from on top of a base. In an arena shooter the maps should matter.