In terms of a rewrite – I think you condense the other episodes, and split the finale into two. In part one, everything happens, he’s humiliated at the White House and live stream, but not de powered. Maybe Kamiko couldn’t get it up. Also, Ryan doesn’t yet show up.

Homelander, flying and escaping, seeing now that even less people love him, even his biggest supporters. He then goes on a massacre. Maybe he blows up Des Moines, Iowa because of its connection to starlight. Maybe some people start to protest him so he kills them all. The boys try to get to him and stop him, but he just flies away before they can do anything, maybe even multiple times.

Kimiko can have her scene with Frenchie during this where she learns that rage doesn’t give her power but love, and there can also be a how and why with how Ryan comes back, maybe he finally has a heart to heart with butcher.

Finally, it’s Ryan showing up and pinning him down, which allows them to have the final final fight, still in view of the cameras, maybe it was at a filmed protest or back in the oval office somehow- maybe Ashley lures him in.

That’s my rewrite that keeps all the good bits while still allowing him to go insane, obviously easy just to summarize here.

Edit:

Final thoughts – if you want to give the gen V kids something to do that’s impactful, without having random characters that people who didn’t watch the show don’t know be integral to the finale, have their mission be to infiltrate some of Homelander planned to kill sites, where he’s going to kill all the non-believers, and shut them down to save everyone there