I always enjoy these updates to your Warrior. There's loads of great stuff in it and I think it all works really well for what I always felt the baseline Fighter should have been.
If I was to get nitpicky on a few things (none of which are deal-breakers, but merely just my own personal picadillos on how I like to see things), here are a couple comments:
Cavalier: For what it is intended to do, it works great. My only issue with it is really just a philosophical one, which aligns kind of like what the issue used to be for Rangers and Favored Enemy (but which was fixed in 5E with the Hunter subclass). Mainly that the kit gets its abilities in only one particular way-- on the back of a mount. Which means that for however much of a percentage a DM chooses to run his campaign where being mounted isn't an availability to that player (dungeons, inside castles etc.), this kit is useless. Just like when so much of the older Ranger's special combat stuff used to only work on their Favored Enemies, meaning that any fight that wasn't against their Favored Enemies they were without anything special to do.
5E fixed that for Hunter Rangers by giving them abilities that were flavorfly intended to illustrate a type of favored enemy (say, oversized creatures, or hordes of mid-sized creatures) but which had a much wider range of time they could be used. Not ALL the time, obviously... but enough to know that the ability wasn't going to be shut down on you for 85% or more of the game (whenever the DM chose not to throw a specific type of enemy that you happened to be favored in.)
In many ways, I almost wish there was a way to accomplish that with the Cavalier as well... a trio of abilities that are flavorfly intended to invoke being mounted (and perhaps even be better while mounted due to the natural advantages being mounted gives you in certain abilities)... but which could still actually find use when not (since so much of the game never actually is except in very niche campaigns.) What those kind of abilities are? That I have no idea! LOL! It'd be one of the more difficult kits to design I would imagine (and why it seems most people don't even try.) Abilities that are usable while on the ground and which feel like they are representative of the mounted combatant... and perhaps actually just get better and more powerful when the player actually does get up onto the back of a horse. The hard part being finding that line between not being too overpowerful when mounted, but then also not completely useless when not. It's a big ask!
Knight: You straddle the line in the names of your kits between descriptors (Deadeye, Slayer, Vanguard) and "occupations" for lack of a better word (Cavalier, Marksman, Scout, Warlord). I like pretty much all of them you've used except the use of 'Knight', because that's the only one that to me has standard fantasy roleplaying essence and story layered on top of the word that does not necessarily apply to the type of warrior the mechanics are geared for. Ask me what a 'Vanguard' is, and I could come up with a generic explanation of what it might represent, and the mechanics of the archetype you give it would certainly exemplify that. Ask me what a 'Scout' is, same thing. 'Swordsman'? Other than the specificity of weapon choice in the name (and that not being a necessity for the kit), same thing.
But with 'Knights'... I always have an idea of what 'Knights' are, how they act, how they become 'Knights', how they are represented in the fantasy... and it's always more than just "guy in platemail and shield, typical Tank". 'Knights' as an identity are more than that, which is why I appreciated it becoming a specific Background, rather than being used as a generic type of warrior. And also why I think 5E chose the word 'Sentinel' as their feat that gave out the "tanking" abilities we've come to know. So me personally? I think I'd like the kit be called something like 'Sentinel' rather than 'Knight', just because there's a story aspect in most worlds to being knighted and becoming a Knight that just aren't tied to this kit. Small nitpick sure, but one that does get to me.
Scout's 'Marked... for Death': For some reason this just doesn't really work for me as an ability for this specific kit. Being able to grant Advantage to every other ally is a powerful ability, and I don't know if I'm buying the reasoning why a Scout is the one who gets to have it (and how he accomplishes it.) The maneuver talks about "marking" the target, but what exactly does that mean in the context of a ranged weapon user? Does the Scout hit the target with a special "light up" arrow that makes it easier for everyone to see and hit the target a la the Guiding Bolt or Faerie Fire spells? Nope, because the attack the Scout gets to make that he foregoed his Advantage for doesn't even need to hit for the Advantage for everyone else to still work. Is it that the Scout is kind of telling everyone "Hey, I got this guy in my sights! Everyone attack him!"? That kind of sounds more like an ability the Warlord should have, if it's more a verbal tactical indicator that makes it easier for his allies to hit the target.
And then mechanically... due to the ability of gaining Advantage by Hiding and then attacking from hiding, ranged attackers are usually much more likely to get Advantage during combat. So you couple this 3rd level Scout with two levels of Rogue for Cunning Action... you now have a PC that can Hide with a bonus action (needing only Lightly Obscuring terrain due to the Scout's first ability), attack with their Acton with Advantage, and then forego that Advantage to give everyone else Advantage on their first attack against the target for the round. Every round for the entirety of the combat. To get all that without even a really plausible explanation "in-world" of what the Scout is doing to create that opportunity? Not really sure I like it. I think it's just too powerful for what a non-spell can do and how often it can be done.
And then finally... as the 5E Feats are not actually included in the 5E SRD... I dunno if you really want to include them verbatim in your document. Granted, if you don't intend on putting this up on DMsGuild and instead just have it out in the ether of the internet for general consumption, it might not matter. But you might want to take them off anyway just in case?
Great work!