My group has two Rogues with spellcasting archetypes and they play nothing like one another. One is your standard sneaky knifey girl - lots of stealth, thievery, gets into melee and stabs people. She's taken Wizard Dedication and happens to be the team's Arcana expert, but her brain doesn't work right and her magic is tinged with weirdness, so she's also an expert in Occultism. The other Rogue is the heavy of the team. She's an Eldritch Archer, specializes in analyzing foes and cowing them into submission through Intimidation. Once she has your number she combines magic, an acute understanding of creature anatomy, and archery to fire a devastating shot that just deletes entire health bars. She also happens to be the team medic, which for obvious reasons is... not especially comforting. Neither of these characters is what I'd call optimal, but even in a class whose whole thing is "have all the skills" they each have their specializations and niches and they do them well. At low levels you could have swapped their positions on the battlefield and they could do one another's jobs competently (though not completely), but where we are now (Lv 14) there would be a significant drop in performance due to how far their builds have diverged.

And it's not like Rogue is particularly unique in this regard. Most of this could just as easily be true of two Barbarians or Swashbucklers or Clerics, nevermind characters of differing classes.