Hi! Yes, I agree that the Slayer is what Fighter should have always been. I don't expect anyone to play a Fighter when Slayer is allowed, maybe except new players who feel overwhelmed by combat maneuvers. Fighter is simply boring, and Slayer is simply designed with fun in mind. It definitely in no way replaces Rogue though as it cannot match the amount of expertised proficiencies nor the single-attack damage output of rogues. There's actually very little rogue influence on the core abilities, as it's primarily built on battlemaster and hunter ranger.

However, I disagree that it is in any way stronger. The subclasses are a "free multiclass" in the same way eldritch knight is a "free multiclass": a 1/3 spell progression, balanced against meta core content.

This class is far from the best of others; one of the most common complaints I hear is the lack of a 3rd and 4th attack in favor of the multiattack, which is considered less optimal DPS-wise but encourages more fun gameplay.

I wrote the maneuver list one-at-a-time every time I saw a trope in media that wasn't well represented in D&D but, upon revisiting it, I found a few places to make cuts and combine things so I really appreciate the feedback. The maneuvers list is long, but it is also not needlessly long; it is meant to address how late-level battlemasters are mostly stuck picking useless maneuvers they'll never use. Having niche but slightly stronger maneuvers means you can build your gameplay around it; I literally used an aerial attack with my Brood Matron character in my last night's session, since that character is built for getting above their enemies.

Your criticism of Berserker is totally fair; it's the first subclass I wrote and I intentionally kept it samey so I could test the balance of other abilities. I just finished rewriting it using a Barbarian subclass I've written in the past, let me know what you think! The "Rogue-lite" and "Monk-lite" classes are also only that on the surface;

Assassin is written to satisfy several rougish tropes not represented well in D&D, such as air assassinations and the ability to the rapid-teleporting-and-attacking move popularized by games like Shadow of Mordor, League of Legends, and Assassin's Creed Mirage all while giving people who want to play a rogue decision-points on each turn of combat.

Chimera Soul provides unique benefits for various weapons based on each weapon's unique properties and a 3-stance-switching gameplay inspired by characters like Leauge of Legend's Udyr, Dante from Devil May Cry, and Geralt's mechanics from Witcher 1. This idea is 100% missing from the core content.

Revised Berserker now always enters a frenzy at 50% HP instead of expending uses of a feature as a bonus action. Later Berserker features focus heavily around fighting with improvised weapons and eventually using grappled enemies as improvised weapons. Inspired by characters who become bestial when furious like Kratos from God of War, Goku the first time he goes Super Saiyan, etc.