Define ‘super secret #1 Legend deck builder’ — and remind me who said anything about a concept like that in the first place.
In contrast, there’s this particular notion:
Yeah, surely bragging, especially to random characters on a forum, is the most mature, wise, well-adjusted and rational course of action. 
Anyway, while I’m at it, back to something serious.
I’ve added ‘among others things’ for a good reason — that wouldn’t be enough. Moreover, just analysing a lot of real games and presenting results isn’t probably the way to a ‘perfect’ solution — if nothing else, due to a feedback loop that it introduces, making the results somewhat biased. Instead, something akin to AlphaZero (AlphaGo, AlphaStar, etc) likely is: the AI would master the game from scratch, just by playing a lot with itself and learning, then wreck the ladder or present the ‘ideal meta’. Of course, this would also take the last bit of fun away from human players… and these computational resources are better spent elsewhere, to be honest 
— after all, a game like chess is just a toy for it.