Thanks for sticking it through!
The final stage wasn't going to be like that, but a lack of time made it easier to just place a lot of enemies. It took me a while to clear it as well during playtesting, but I just assumed "the player will not try to rush through this to check if the ending cutscene works while under time pressure, so surely it's fine?"
Maybe we could say that it's some kind of meta-reference: causing trauma to the player to make them more strongly connect to the umbrellas? To hide the fact that there wasn't much artistic intent behind it. Yeah, that's my story from now on. Totally intentional.