The chain gun warthogs in every Halo since H3 have been underpowered. Especially in 4 and 5, a single plasma grenade was enough to destroy a hog. Add in the fact that plasma pistols are easy to get in H4 and H5, and the warthog no longer strikes any fear into the opposing team, it’s looked at like as an easy double kill.
In H3 a chain gun hog could be stopped, but also could wreck havoc if the opposing team didn’t strategize to shut it down.
TLDR, the hog takes 2 Spartans to operate, and should be a net force multiplier. Every game after H3 made the hog feel LESS effective than two Spartans on foot.
Agreed about the reduced vehicle durability and increased vehicle vulnerability to infantry weapons being a hindrance to vehicle performance. While we're at it, let's not forget about how the Hog is light as a feather, easily prone to being tripped up by a pebble - to use an extreme example. This became abundantly clear in Reach, although the sentinels and carriers in the H3 Hog run also represented a menace to driving. Plus, ramps were almost suicidal to drive over. The Hog could really use more traction, if that's the right word for it.
Two other gripes I've had with the Hog over the years: inconsistent splatter (an issue with vehicles in general actually, i.e. you could be driving full speed at an enemy but due to a slight angle adjustment or terrain shift, it doesn't do any damage) and reduced effectiveness of powersliding (I'm thinking mainly of H3, but it could also apply to other halos i.e. difficult to parallel park, can no longer fling yourself out of the seat without risking splatter). Although I appreciate the ability to swap seats without having to get out, that was a good addition. Sure beats driving the Hog straight forward and using the momentum to jump into the turret.
I noticed most of the Hog's variants in H5 were purely cosmetic or merely featured different projectiles and some other minor differences. How about making the "Turtle" from H3 Forge an actual thing? Back then, it was a simple setup with two UNSC shield barriers placed over it. I seem to remember it being sturdy enough to fend off the lasers from the Sandbox guardians (as long as you drove really slowly).
There was also a modded Hog hovercraft featured somewhere on YouTube.
Edit: SectionUnity beat me to it. Yea the Hog flips too easily, it could use more stability.