> Users who go to http://mysite.example/ would be "redirected" to https://mysite.example/ but that redirection wasn't protected so instead the active bad guy ensures they're redirected to https://scam.example/mysite/ and look, it has the padlock symbol and it says mysite in the bar, what more do you want?

You can do better than this. You can have your mitm proxy follow the SSL redirect itself, but still present plain HTTP to the client. So the client still sees the true "mysite.example" domain in the URL bar (albeit on plain http), and the server has a good SSL session, but the attacker gets to see all of the traffic.