__________________ "Happiness is a lie. Life is horror. The light is always dying all across the universe. The last star will flicker out someday, when it does, all that remains is shadow. And I will be its king!"'-Amahl Farouk
The issue is Kanan had a fully fleshed out backstory that was well documented, and not that old. A 12 issue series that's only 5 years old isn't something you retcon on a whim, which they clearly did(or outright ignored) just so Kanan could show up in the Bad Batch's story for a bit.
And unless they're gonna retroactively show Squad 99 interacting with the Rebels at some point, it wasn't even for any good reason.