It'd be like making Godfather 2 a stoner comedy.

And that's how you get terrible comic strips

You just described every single attempt at homemade pizza i ever did

No!

If it was just "Fortnite but a bit better", then very few people would play it, as having a lot of people to play against is important and network effects would keep them on Fortnite. (See also every other "X-killer" - Facebook killer, WhatsApp killer, e-Bay killer, etc. A slight improvement will not do.) Also, Fortnite wasn't really the game it is until they cloned PlayerUnknown's BattleGrounds into it, so it needs to be:

• something with a really compelling gameplay loop that's good with a few people but gets better with more people

• not a Fortnite clone, nor something that could be introduced into Fortnite as a game mode

Like you say, just a clone will not do. Need some really exciting innovations in gameplay, which is not Ubisoft's thing, to put it kindly.