-
The mech hanger being that little bit bent wouldnt put you 3 cogs in, and from what I can see there is no other obvious bend /twist to the body.
This might be daft to ask ... but have you tried turning the pedals / chain since you released the cable? If it's not the limit screw or muck holding it in place, a chain (partcularly an old stiffed up rusty one) will do that just fine if theres no rotation made to allow the derailleur to guide chain back down to high gear.
If thats not it, as @M_V says, back out the L + H screws βΒ next port of call should be to get it off the bike and give it a really good clean, lube and flex all the spring / jointed parts.
Thanks! Will give it a go. Am starting to think the mech hanger is off though.