Why are you saying this “Game Freak would do this, Game Freak would do that” when the last non-Let’s Go remake they (not ILCA) developed came out almost ten years ago, so we don’t have anything else to go off of that’s more recent than that. I consider Let's Go its own thing that doesn't really show how a future remake would work.
I would say that ORAS as "took the original versions and greatly improve[d] over them, the only major reason anyone has for liking Emerald more is the battle frontier. I think that if Emerald had no battle frontier, nobody would argue ORAS was worse. I don't think the same would happen for BDSP if Platinum didn't have one.
English is not my mother tongue, and while this can also be the case for you, maybe you are simply better at it than me. I say this in case that you want to unnecesary correct every mistake I make with those "[]", even if by context it's perfectly understandable.
You asked me what am I taking into consideration when making those asumptions if 10 years have passed since the last remakes. I don't know, have you heard about Pokémon Sword and Shield? Or about Scarlet and Violet? Or, why not, even about Sun and Moon, or X and Y, or the absolute decay of the franchise in the last years not only in terms of quality but in raw content too?
Do you remember how not a single Battle Tower exists in Pokémon Gold and Silver (only in Crystal and it is substantially different from the one we know now), yet they added not a Battle Tower but the entire Platinum Frontier into the games just because they could? And do you remember how they didn't add the Battle Frontier from Emerald into ORAS because "they were mostly based on Ruby and Sapphire"? Oh. Fine.
"I think that if Emerald had no battle frontier, nobody would argue ORAS was worse". Yes, and I do think that if my grandmother had weels, it'd be a motorcycle. But my grandma is still my grandma and Emerald has Battle Frontier. I don't know what the point of this "if this reality didn't happen and this reality I just made in my head existed in its place... [insert favorable point]". Yes, and if a great game were trash instead of a great game, it'd be trash. And if someone tall were short, it'll be short. And if something good were bad, it'd be bad.
The point is the Battle Frontier of Emerald in itself was absent from ORAS, while the battle frontier from IV was present 2 generations earlier. Now imagine after Sword and Shield or Scarlet and Violet, games that are just Pokémon Go with raids and normal gyms lol.