Parmandur
Book-Friend
Well, sure, you swap out the d10 HD, certain fighting styles, action surge, second wind, and Extra Attack...
...or, you could start with cleric and swap out spellcasting, channel divinity, divine domain, destroy undead, divine intervention...
...or Bard and swap out Spellcasting, Bard College, magical secrets, and re-skin 'song' of rest...
...and add 6 or 8 or so Archetypes...
Well, no, the point of the variant Class Features (I'll call this "Kits" for now) is to work with the same Subclasses: so a "Warlord" Kit might replace a number of Fighter kill-y features for support-y features, but your could still have a Cavilar, Samurai, Champion, Battle master, etc. as a Warlord.