I agree. Literally my first complaint about XY was how your first wild Pokemon encounter on the first route was ... a damn Pidgey. WHY WASN'T IT A FLETCHLING, GAME FREAK!? It was a scripted encounter, too, they had control over it.Having old pokemon in invalidates the goal as you are aren't surprised or excited of seeing an old pokemon in a new region.
I do have my favorites across all generations (e.g. any hint of a wild Eevee, Shinx or Riolu and I will beeline right over there, even if I don't use them in party) but on average the majority of Pokemon you encounter in that region should be ... y'know, native to that region? Look at the list of wild Pokemon in Alola Route 1 - only 2 of 6 are Alolan natives (+1 if you count Ratatta's regional variant).
Gen 5 had a huge Pokedex partly because, as a design decision, Game Freak decided that BW1 would not feature any old-gen Pokemon until the postgame (plus there was the Dream World thing). It was a useful choice, but it did mean they had to come up with more "dex filler" than normal.