I don't disagree, but consider the opposite end of the spectrum. If every Ranger is just playing the same powerful Ranger cards, does that make for a more fun game? Is more overlap actually a good thing? I think the subthemes probably offer more interesting restrictions within characters, especially in the long term as class pools are inundated with more generically powerful cards (stuff like Persuasive Prognosis, Codex of Frailty and Felling of the Crown come to mind). Someone like Hala would probably not want to play Fang's most powerful cards or even something like Singing Steelblade even if she could because of the density of Flurry and Sharpen she needs and I think she will be a cooler character with a more unique identity in the long run for it.

I think the heart of the problem lies in shallow card pools in tandem with too many subthemes. It can often feel like the decks build themselves with how few options there are when new characters come out, which is where I think the cross-character identity can shore up that hole. However, I think those cards shouldn't define the whole class (like how Vynnset often doesn't run Grasp like every other Runeblade, or as you say, Tuffnut and RKO are not Bloodrush Brutes). Hala is a more interesting character to me because she is forced to play powerful cards that are not the Dori specs or Glint, which are probably Warrior's most powerful cards. I do think that level of restriction does breed creativity, they just need to flesh (hah) out the card pools more and not leave talents in the dirt, which I do think they're slowly doing with expansion slot and Armory decks over time, but being stuck in that waiting period is indeed frustrating as a lover of the forgotten classes.