Regarding to? Speculation? The number of mons Ash catches by gen? to do a quick recap of the past 6 gens:
Johto: Heracross, Bayleef, Quilava, Totodile, Noctowl, Donphan (6)
Hoenn/BF: Swellow, Sceptile, Corphish, Torkoal, Glalie, Aipom (6)
Sinnoh: Staraptor, Torterra, Infernape, Buizel, Gliscor, Gible (6)
Unova: Unfezant, Oshawott, Pignite, Snivy, Scraggy, Leavanny, Palpitoad, Boldore, Krookodile (9)
Kalos: Greninja, Talonflame, Hawlucha, Goodra, Noivern (5)
Alola: Rowlet, Lycanroc, Incineroar, Naganadel, Melmetal (5)
Journeys (so far): Dragonite, Gengar, Lucario, Sirfetch'd, Dracovish (5)
So far Journeys is keeping the pattern of all regions except Unova, and I only expect Ash to catch 1 or 2 more, including Kubfu.
I think it was silly back then and it's silly today to expect/speculate that Ash is going to catch every mon in existence especially now that we have a co-protagonist whose goal is to catch Pokémon.