Halo 4 Legendary (Campaign or Spartan Ops (especially)):
Shoot Knight. Knight teleports away while 5 others continue attacking. First Knight regenerates as you continue the process with several other Knights.
Shoot Watcher. Watcher flies away while 5 others continue attacking. First Watcher regenerates as you continue the process with several other Watchers.
Now throw these enemies together with Crawlers/Covenant all over the place and you have quite the boring experience on Legendary.
I recently played the Halo 4 campaign on Legendary solo and had no real issues with any of those, aside from having to kill the Watchers first being boring.
Multiple Knights? Engage one at time, or split them up (a grenade or two does this nicely usually, if there's space for it). Killing must be done quickly, preferably with a powerful weapon, or having the useful Plasma Pistol (not possible in all missions unfortunately). Usually i ended up using the Lightrifle alone, scoped it drops an average Knight's shield with eight shots, with a pair of shots to finish it. Not terribly efficient but worked often enough for me. And usually i did have a power weapon too, but i always save those for bad moments or bigger fights.
EDIT i can't recall running out of ammo but once, and that was due to me shooting badly in the previous encounter. Didn't have ammo problems the first time i played Halo 4 either. I don't get the complaint of the game having too little weapons/ammo.
Why would you be playing Halo PC BTB seriously? That's the important question here.
I play to win. Fooling around i save for campaign on Easy, or a custom game that is set up specifically for fooling around. Anything else, i play seriously and to win. EDIT and i've always done this. If i don't play to win, why would i play at all?
I think we're playing different games buddio. It took some skill and understanding to use a Warthog successfully; it's definitely not as easy as Tawpgun implied earlier (against decent players anyway). The vehicles in that game were pretty balanced IMO.
You had to learn how to control the fishtailing (by incrementally nudging the right thumbstick based on the degree of the turn instead of one sharp turn/swipe) and use the momentum/physics in your favor.
And i was mostly talking about the campaign. It is goddamn frustrating when any vehicle get stuck on a small bump, a rock, or a corner, or bounces away from one. And i'm not talking about a slight bounce you can correct with controls, but the type where you can't do a thing until it slows down enough you might be able to land wheels down. What's annoying is that either kind of bounce may happen from full speed, or even slow speed (and in multiplayer, combine with awful netcode (Halo PC didn't have the greatest code there is) and/or lag...).
Not that later Halos are immune to odd/bad geometries, or occasionally wonky physics (flipping Warthog over only for it to land sideways or something).
In multiplayer (Halo PC), i usually flew a Banshee or drove a Ghost, or i was a Warthog gunner (honestly, i'm not great 'Hog driver, i'm merely okay but i'm much better as a gunner). Or i found a power weapon and used it.