Shadow Tag in general is more or less banned, originally because of that one glitch but now because Shadow Tag is the reason why Wobbuffet is banned to begin with. Shadow Tag as an ability is banned I'd think (everyone who uses it makes heavy use of it), but Speed Boost as an ability is not.
There's no double standard with enforcing a ban on an entire ability/move, but on a specific move on a specific Pokemon is where the double standard applies.
But they didn't have to ban moves, so how is lugia with banned moves relevant to a banned ability on Blaziken?
Okay let me rephrase this.
You're not allowed to use two abilities in tandem, correct? Drizzle and Swift Swim are the two abilities in question that I am thinking of. That is easily enforceable, there's no double standard because it's an ability (combination) ban.
My Lugia example was extremely hypothetical. You cannot ban a specific moveset of a Pokemon because that's apart of the Pokemon. It allows us to open up a double standard that complicates tiers, such as "we can easily place x Pokemon in a lower tier if we ban a certain moveset." So, let's take a Gen IV Scizor for example; Swords Dance/Quick Attack/Bug Bite/Bullet Punch or w/e (i haven't played competitive in a while, bear with me).
You could ban that set and Scizor would easily go to a lower tier... same concept as banning one specific set on one specific Pokemon. In this case, it's one specific ability on one specific Pokemon; it's far too specific and is probably not easy to enforce especially because one of Blaziken's innate abilities is now Speed Boost. With Shadow Tag, yes it's an innate ability of three Pokemon, but those three are SO dangerous and overpowering with it that the ability itself is restricted to Ubers, which wasn't the case for Speed Boost. Competitive politics are extremely complicated but it makes sense if you read into it.
But Shadow Tag isn't even banned anyway so who cares