True enoug, but the main reason i believe that exca's ban fueled Ho was for one reason.
I call this the "mega super sweeper theorem."
It basically states that a large portion of the metagame will gravitate towards the most powerful sweepers.
Since exca(And thundurus) were banned, the next super sweepers were d-nite and volc, and of course deoxys-s suddenly became much more useful.
Exca's ban also fueled HO because Excadrill single-handedly made many HO staples, such as Scarfers, unviable.
Thunderus could have stayed in OU, and we'd still be seeing a HO metagame, even with Priority T-Wave being thrown about.
The problem is, in a HO metagame, where high powered sweepers are dukeing it out, relying mostly on resistances [Except in Dragonite's case] to get in and set up, Screens are INVALUABLE. And Deo-S basically can set at least one of them up, guarenteed, at the start of a battle. Especially as it can set up whichever screen stops your foe's check, due to team preveiw.
Ie: You see someone who's team is Volcarona weak, but they have a Gyarados. You set up Reflect. All of a sudden, Gyarados can't come in and beat Volcarona so easily. Either Volcarona runs through half the other team while Reflect is up, then it gets KO'ed by Gyarados, only for a different teammember to clean-up, or Volcarona sets up and runs through the whole team because it's too late for Gyarados to do squat.
Then you see someone who's, say, Dragonite weak, but is packing Latios. So you put up Light Screen at the start of the match. You get the picture.
Also, Deo-S can Screen and set up one hazard, if it chooses to go fully Suicide/Suppport. It's not like you can Taunt Deo-S unless you're Whimsicott... and it's not like Whimsi can do much to Deo-S anyway.
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Please note, that Deo-S can also do a lot more than Screen. There's the hazard based sets, the Stallbreakers [Recover/Taunt and 2 Attacks screws Stall over so badly it's not funny], and Cleaners [LO + 3 or 4 Attacks]. All of which are basically unstoppable at whatever their set is designed to do. Deo-S is basically a Jack of Many Trades... and pretty masterful at all of them! About the only things it can't do is outright sweep, and obviously, Stall.
No single set is the problem. If we were banning Deo-S for hazards, we'd be banning Ferrothorn and Forretress, beause they can set them up as well, if not better, over the course of the game. If we were banning purely for screens, we'd be seeing Espeon, Azelf, and possibly Bronzong and Renkulus go. If we were banning for being a cleaner, Starmie.
But it's not
one set. It's the culmination of all of them, like Gen 4 Mence. If you get the set wrong, you are going to be at a massive disadvantage through the remainder of the game.