I actually agree with XBF4N on this one.
The thing with Halo 2 is that, while there's no denying that it's unrelentingly brutal and unforgiving, there's an awful lot of 'fake' difficulty - the gameplay isn't challenging so much as trial and error, or outright luck-based. There are more than a few sections where enemies are spawned right on top of you, or behind you, or respawn infinitely, or are placed in such a way that you have to start reacting to them before you're even aware of them if you're going to get past them: their presence isn't even telegraphed or hinted at beforehand most of the time. The last of these is completely against the idea of difficulty as ideally anyone sufficiently skilled, aware of their surroundings, and understanding of how best to use the game's mechanics and the tools which they have at their disposal should be able to complete a section on their first attempt. On Halo 2, this is often literally impossible, as without knowing exactly how, when, and where certain AI triggers operate, you will be killed simply because there are only one or two very specific courses of actions which result in success, and you're not likely to be following those on the first attempt because there's no reason to take them.
As for Knights? I like them. And I don't really get what people mean when they say they fight Elites with 'tactics', when really what they mean is they jump and strafe side to side while tapping at the Elite with a mid-range headshot weapon until it dies, or using the noob combo. Those are both very sensible ways to fight an Elite, but as tactics go they're fairly straightforward and simple.
And the thing is, Halo players have gotten really complacent over the years, which is one of the reasons I hate the BR so much: it's our solution to everything. Squad of Grunts? Strafe with the BR. Pair of Elites? Strafe with the BR. Group of Jackals? Strafe with the BR. It's not uncommon to see players refusing to pick up something as powerful as a Shotgun or a Sniper Rifle or even a Rocket Launcher because they don't want to lose their BR, and that should tell you everything about how much of a crutch it is for us. Very large portions of the playerbase even insist on starting multiplayer games with the BR, because they're so dependant on it that they don't actually know how to use the other basic weapons!
I think this is why so many players hate Knights. It's because they're one of the few enemies that you can't just kill by strafing with the BR. You're forced to actually do something different to the usual, lazy and repetitive approach to combat - in fact, they're one of the only enemies in the whole series who're more vulnerable to automatics than precision weapons. Even higher-ranked Knights can be taken down with a single magazine's worth of fire from the Suppressor, and provided your aim and awareness are good, assaulting them directly is actually a very effective tactic even on Legendary. But because we're so hopelessly addicted to the idea of strafing with the BR, when we come up against an enemy who that doesn't work against and we have to actually play with a tactic that's from outside our comfort zone, we accuse the enemy of being unfair and bullet spongey when in fact, they're just resistant to one particular tactic.