No matter what you think of Halo 5, due to all of the extra movement and options available the skill ceiling is a *lot* higher than it is in the others.
that doesn't make for a good game tho. the game feels super clunky and the extremely low FOV doesn't go well with a game that makes use if boosters and sprinting all over the place
and I also disagree with that skill ceiling being higher to a point. due to the mobility it's way less important to have map knowledge and map control during a match.
and due to the fact that basically every ability you have in Halo 5 lowers your gun while using one of them also lowers the skill ceiling to a degree as you basically can't use these abilities during combat. you can only use them to evade or run away in most cases.
if Halo 5's abilities didn't make you lower your weapon and you could always fire while using them, you might have a point, but as it is you can't really combine abilities and combat in any skillful way.
it's basically:
[I sprint, I stop sprinting, now I'm shooting which locks me out of sprinting]
[I shoot, I stop shooting to use my thrusters because they lock me out of shooting, I start shooting again]
and with these abilities in play you are forced to use them or you are at a disadvantage.
meanwhile in Halo 3, because there are no abilities that slow you down or make you lower your weapon (locking you out of firing your gun), you have your full range of movement DURING active combat.
in Halo 3, because everyone always moves at the exact same max speed, it is a viable strategy to walk backwards and shoot at a distant enemy while simply traversing the map to get to an advantageous spot.
In Halo 5 that isn't necessarily an option because players have sprint, and you are basically firced to use sprint to get to a power weapon as fast as possible... so you are locked out of actively participating in combat during that. not so in halo 3 where it's a big part of the skillset to traverse towards spots while also firing at people.
this means walking backwards, doing blind jumps, maybe even trick jumps, is a skill you can learn that gives you a huge advantage in Halo 3, but not in Halo 5.
In Halo 5 it's more optimal to just sprint forwards and use clamber to get up to high spots, and that's almost never in any way hard to do either.
so I would argue advanced mobility lowered the skill ceiling dramatically in parts of the game, while only marginally lifting it in other parts.