NPC Warrior will outdo many of the PC warrior classes in many cases...
OK. Let's check this. The Warrior is a cut down Champion Fighter who at low level gets Martial Role in place of a fighting style and Action Surge. They don't get extra ASIs and their third attack is delayed from level 11 to level 15
At fifth level they are fairly comprehensively behind; they get their extra attack a level late. At sixth level they close the gap - but are either an ASI behind (which adds to hit and to damage) or a feat behind, which can be a gamechanger. So we can say fairly comprehensively that from fifth level onwards the warrior has fallen behind the champion fighter.
The question is therefore at 1st to 4th level. At third level and fourth level the champion and the warrior gain the same things (improved crit, ASI), and the fighter's level 1 second wind is gained by the warrior at level 2 so we only really have two cases:
L1: Fighting Style + Second Wind vs Martial Role
L2-4: Fighting Style + Action Surge vs Martial Role.
We can also say that the warrior's Defender martial role is worse than the Protector fighting style even if Protector requires a shield; it's easier to be next to your ally than your enemy when dealing with archers.
So this does leave Attacker. +2 to hit vs the archery, great weapon, or duellist fighting style
and either Second Wind or Action Surge.
At first level the fighter's advantage is huge. Second Wind is 1d10+1hp and is likely to increase the fighter's hit points by 50%; it's implied that the warrior gets rolled hp (and doesn't get the half rounding up each level). At first level second wind is huge and probably bigger on its own than +2 to hit.
But let's put Second Wind Action Surge to one side for a minute and look at the fighting styles. Attacker is easy to calculate; through the magic of bounded accuracy +2 to hit when you hit on an 11 is an increase of roughly 20% of your DPR.
Archery: Archery fighting style with its +2 to hit at range is strictly worse than +2 to hit - but it's not very much worse if you want to be an archer. Action Surge with its explosive damage should be far better overall than +2 in melee for a specialist archer. And the ranger's just going to laugh at you.
Duellist: Taking the textbook duellist with a longsword and shield, the warrior should be doing 1d8+3 damage in melee or an average of 7.5. The duelist is going to be doing 1d8+5 or 9.5 on average. Even if we allow at 4th level a first ASI and a +1 sword it's 9.5 vs 11.5; the duellist fighter still hits more than 20% harder than the warrior so they do more damage per round.
Great Weapon: This one is closer. The warrior with a greatsword does an average of 10 damage on a hit before 4th level (2d6+3). The average damage from a greatsword hit is 3 + 25/3 = 11.333. Now I'm absolutely confident here that the action surge closes the gap in terms of dpr against being 20% more likely to hit. For a polearm (8.5 vs 9.3), a strongly suboptimal weapon without Polearm Master, action surge closes the gap (and is thus stronger thanks to being burstier and more front loaded) if you manage to have a rest for every ten rounds of combat. And you don't really have the hp to take ten rounds of combat without a rest.
So from level 2 to level 4 the warrior is a second rate champion fighter but not far off. From level 5 onwards the champion pulls away and never looks back assuming feats are in play.
I don't see why Martials don't get the extra bonuses to hit...
Anyone who thinks a Wizard (or any other class) can't get a 20 STR or DEX is kidding themselves...because 20 is the max, you HAVE to eventually put your stat increases SOMEWHERE if one is not using feats...and not everyone uses feats.
And anyone who thinks that a level 5 wizard is remotely as good with a sword as a warrior with is kidding themselves. Extra attack is huge.
If something is good enough to give to the Sidekicks, it should be good enough to give to PC's
The goal of sidekicks is simplicity so you leave anything you need to remember off the menu. So you have a significantly weaker class overall. The only worry here is multiclassing cheese.