I recall in one of the Star Wars books that there is an untouched portion of Coruscant. Endor could be repurposed as the untouched small part on Endor, where the shield generator would be hidden.
It makes sense for the Empire to hide their super important shield generator in a forested part of the planet where people don’t live or go to. I know the untouched part of coruscant was actually deforested before the OT but you would only know that if you read Catalyst.
So, perhaps the Death Star 2 is being built and they discovered this and decide the only way to survive is to freaking zerg rush the capital in a last ditch effort to win because if they finish the Death Star 2 then they believe that the war would essentially be over. I like the idea of putting the Luke-Vader fight being put on the same planet as the Rebels heading for the shield generator. And then instead of Luke pulling Vader out of the DS2 he’s trying to get out of the capital before the DS2 pieces fall onto the capital.