It's pretty obvious that a lot of people who criticize ORAS and BDSP for dropping the Battle Frontier have never actually used it. Simultaneously, a lot of people who defend the removal of the Battle Frontier don't actually know what it is either.

One common reason that people cite for why the Battle Frontier should come back or should be gone (depending on their side of the argument) is that the Battle Frontier is aimed at competitive players. The side in favor uses this argument as the game should have features that appeal to different players, while the side in disfavor says it's obsolete now that we can play against other players online. Both sides are in the wrong, as the Battle Frontier is not aimed at competitive players. The purpose of the Battle Frontier is to play Pokemon under unique rules that differ than the usual. Those rules DO NOT mimic competitive play and are unavailable in multiplayer. They offer unique experiences that different players like or dislike based on their personal preferences, but in no way are they aimed at competitive players. Saying that the Battle Frontier shouldn't be in the game because "you can just play multiplayer makes as much sense as saying that Gym Leaders shouldn't be in the game because "you can just play multiplayer".

There is one facility in the Battle Frontier that IS indeed aimed at competitive players- the Battle Tower. But here's the kicker; the Battle Tower also exists outside the Battle Frontier. It was in Ruby, Sapphire, Diamond, Pearl, Sword and Shield, and all the other games just had a similar facility with a different name (Battle Subway, Battle Maison, Battle Tree). So the people who complain about the removal of their "competitive mode"... actually still have their competitive mode. And the people who says this competitive mode doesn't belong in the game... don't realize that the competitive mode is STILL in the games, and it's the non-competitive modes that have been removed.