Yes, why, not how.
Now we see how Tantiss came to be as it was, or at least the closest we've ever seen. And having it as a training/growing facility for elite troops during the rise of the Empire is makes more since than having it be isolated and forgotten by everyone but Palp and Thrawn for years on end.
This isn't polishing a turd, this is Filoni and Fav trying to set things up to effectively erase the sequel trilogy using the 'World Between Worlds' from Rebels to show how alt timelines can exist in Star Wars.
Fact is it sounds like their is a plan for an live-action Ahsoka trilogy in the future, the Rogue Squadron movie, and bunches of shows.
Filoni and Fav are going to try to reconcile the old EU with the new Canon, and so far they aren't doing a bad job of it. Trying to keep them old EU and the new canon completely separate is pointless, and only give KK what she wanted. What Filoni and Fav are doing is effectively undoing and rewriting canon to erase those horrible films.
You missing the point; Mount Tantiss isn’t supposed to be a heavily fortified military base, it’s supposed to be a top secret warehouse, more or less.
Mount Tantiss was originally the site of an
Old Republic fort that was reactivated by
Palpatine during the
Clone Wars.
[2] The storehouse contained both objects and trinkets of unspeakable evil, as well as mementos from the conquests of the
Empire. His most private treasures were hidden in a massive labyrinth designed by
Garrbo V'Droz in the mountain's bottom chamber.
I’ll believe that rumor when I see it and not a moment before. Fact of the matter is, even with damage control being run, it’s a loosing battle. Because episodes 7-9 are going to loom far more in the public consciousness then some spin off films, even if those do get made.
Frankly, I don’t trust Filoni to do it right. Even if shoving his super-special OC in and making her the savior of the galaxy sounds in character for him. I still haven’t forgiven him for the mess TCW made of the Clone Wars timeline. And putting that aside, unless Ashoka is going back centuries, it wouldn’t explain the pre-OT era divergences and so on.
Only way I’d accept it is if Ashoka manages to undo Palpatine’s meddling...but at the cost of removing herself from the timeline, thus moving the TCW stuff into the Disney Wars canon, replacing it with the pre-TCW lore.
Now, it they want to rewrite the Vong War and everything that came after it from Legends, so long as they don’t screw it up, it’s fine by me.