SM-era example: Super-Burst Impact is clearly supposed to be the Johto themed set in Japan. We have two Chikorita and two Hoppip cards in this main expansion. Why? Cut one each of those and we have Sunkern and Sunflora for the first time since HGSS. Random Gen 7 Pokemon (Pikipek, Mareanie), Ultra Beasts (Blacephalon GX, Poipole, Naganadel) and Alolan forms (Meowth and Persian) are tossed in too. Throw out the four Colorless spots given to the Pikipek line in favor of Sentret/Furret and Teddiursa/Ursaring. Rework a few other things and you free up spots for those cut Alolan Pokemon in the subsets or another main set down the line. But the people in charge of the TCG just don't really approach things these way and it's frustrating.
While I agree with you that it is a bit random for them to have 2 of each basic in every 3-staged line (in the main set anyways), I don't think it's very fair to complain that random Gen 7 Pokemon are in the sets. This is the Gen 7 TCG after all, and considering this was both Alolan Persian & Toucannon's 2nd appearance (only after the SM base set) (and Blacephalon's first appearance), I think it's fair to have them in the set, considering they're "only" taking up 12/95 cards.
I like what
@crystal_pidgeot says about the sets theme. Take the Lost Thunder example, while the set includes Pokemon from Alola, they still are in theme (to me at least), with Toucannon flying over Mount Silver and Alolan Persian being in (possibly) Alph Ruins or something similar. That is also why I'm not really that excited for this set tbh. Yes, the art looks good, but I just think the Pokemon featured are just put together randomly. I'd rather have the main focus being on birds/Flying-types (could've had Tornadus Therian GX instead of Keldeo and maybe Archeops/Braviary instead of Naganadel), and then have a few Alola Pokemon (like Bounsweet, Fomantis etc.) on the side
