First, I simply don’t see what the movie adds to the mythos. We already knew that the Death Star has a weakness, and that someone stole the plans and delivered them to Leia. Why does it really matter who made the Death Star or who stole the plans?
The Death Star’s weakness never made sense, and what they came up with to fix that was pretty darn good.
To add to your point, I think a lot of people project their preconceptions of ANH onto RO by assuming that the exhaust port was the built in weakness. But according to Galen, the weakness was actually the chain reaction of a downed reactor.
So in a way, Rogue One actually makes the Death Star’s achilles heal more believable. The Empire may have known they had a relatively unprotected exhaust port that might down a reactor, they just didn’t know that attacking it would lead to the resulting chain reaction.