Scolipede, Geomancy, and Espeon are tools that did not exist three or four generations ago. Even support options like Whimsicott greatly improve the functionality of a dedicated BP. The fact that you don't acknowledge this (and your comparison implicitly argues that it is trivial) raised some red flags for me...
Firstly im going to go out on a limb and say Smeargle is a complete fucking joke. If you use sash you're fucked cos Geomancy takes 2 turns if you use Power Herb....you're still fucked because Smeargle cant set up on shit lol, even with dual screens. This is through experience, its just flat out bad. Ninjask and as thus Scoliopede are similar, that hasnt changed since gen 3. Whimsicott also has so many issues its unreal. Bisharp is omnipresent hell even other Defiant users are still a thing. Magic Bounce is still a thing. Metagross and Diance have clear body pre mega evoing. Memento means it has to kill itself to even be remotely useful. So in order to pass safely, Smeargle needs to hope: Dual Screens are up, SR isnt up (in the case of sash) or the fact that power herb is one use, the opponent doesnt have status or priority or one of the above mons ive mentioned. Seems pretty specific tbh. Things like this are common on offense so its not even "useless niche moves and pokes" tbh that negate it lol.
Also, metagames have changed around DP. BP does not exist in a vacuum. You know why I don't prepare for BP when running an offense? Because I'd rather prepare for people who don't bring tactical teams (as opposed to the rest of the metagame being strategic teams) and I have a ton of other more common threats to deal with. You know, the ones you want to ban.
Ok cool so anything with Taunt that threatens Espeon is suddenly bad and only deals with BP? Things like Taunt MDos, Taunt Talon, Thundurus etc arent useful outside of coincidentally dealing with BP too? Even sets like Dragon Tail Garchomp exist.
Also id like to see the argument for BP being able to set up and switch in on shit like Bisharp, Guesszard, Talon, Thundurus, Gengar etc or shit that hits remotely hard that BP cannot set up on, see: Keldeo and MGardy. Through experience it cannot switch in or set up on any of these things which leads to an auto loss for the BP user which no other play style has. I feel thats a fair risk-reward. This isnt even with "inferior moves" that is just sheer offensive pressure. :\
I can't speak to GSC at all, but it's not exactly difficult to cover everything in Advance. (Also, Zapdos, Skarmory, Suicune, and Swampert are way better than any PHazer available in ORAS.) You have 6 Pokemon and 24 move slots per team. There is a way higher opportunity cost in both team slots and move slots now. Why would any play style, not just offense, want to run a suboptimal team slot or even move slot to deal with a play "style" that reduces the game to a series of tactical maneuvers? People also don't prepare for it because its counters are very specialized and are more difficult to fit into an actual strategy besides passive crit bait, which itself has better things to be running in a metagame that is tremendously hostile to stall.
See above for "sub optimal sets and pokemon" stuff, these "sub optimal mons and sets" as you call them arent even the only way to pressure baton pass as ive said. Also funny you bring up crit bait, isnt Baton Pass itself crit bait? One crit and its again as ive said an auto 6-0 because the whole team goes down not long after.
Also, it's almost too obvious of a point to make, but there's a pretty good chance BP is stronger when it got nerfed twice, once without as much as a suspect test because it was such an obvious problem? It's not even a slippery slope fallacy to say "your logic can literally be used to argue against any restriction on BP in ORAS except Ingrain Smeargle" (which was a years-after-the-fact Advance-specific ban because it was ruining Advance tournaments). So much for "everyone dealt with BP in previous gens. lol.
It's an asinine comparison. Stop making it. The previous generations are not relevant. Period.
There must be a pretty good reason why Baton Pass wasnt touched for the 12 years previously but hey. Also this is the gen when Baton Pass had shit like Mean Look Taunt Umbreon. That doesnt exist anymore and whilst BP has gained some toys, its lost one of the biggest threats over the years. Also stop disregarding past gens, they do have precedent, especially something that has changed as little and as linear as Baton Pass.
The implication of you making this statement (the last sentence) is that this is through some defect (presumably of either skill or mental proactivity in team-building) of the team builder, when in reality, it is ridiculous to expect people to prepare for it, especially when many of the so-called checks you list lose to a lot of BP teams. "Just pack a PHazer." Well, maybe only Skarmory and Zapdos fit on my offense or balance. (Balance doesn't exactly love facing BP either.) Oh, they both get boned by Espeon? Well, that's tough for me I guess.
Again ive listed many things BP cant set up on or beat easily so i dont think its that ridiculous to have people prep for it given ive listed a good 10+ things that BP struggles with both on offense and stall. Also the last sentence is one of my biggest gripes this gen. Again im not arguing for if its broken or not, i just feel people are very lazy and offensive players get what they want. If something threatens senpai offense it gets suspected and banned but if something threatens stall or indeed balance, no one gives a shit because they are narrow sighted and dont care about other styles. Sad but true.
It's just baffling to me that someone who hates the surplus of threats in ORAS and wants to ban many of them is defending the most blatantly uncompetitive strategy in the tier? (Or one of them: I'm not going to argue BP vs. Shadow Tag with anyone.)
Id sooner face teams of BP than any mega and thats being honest lol. Again im not defending it, im just saying "why is it so hard to get one of the many things ive listed above or in my previous post on your teams?" i mean something like MegaGardy alone has less things that deals with it than that thwarts this whole style lol.