I concur with the issues concerning Thor that people mentioned above: he really needs time to set up; & small hand size + expensive cards aren't helping. On top of that, he can't thwart at all with so few minions in most scenario's. Defender of the nine realms just should not be played, as it can easily take some10 cards before one pops up. It's not worth the +1 booster token adding to the scheme that much faster. His starter deck just plain sucks solo. Then again, solo + aggression is simply not a great combo due to lack of threat removal. It's the LotR LCG tactics problem when it was released, but anno 2020.
He was probably designed with multiplayer in mind; and if not, he's great for the people calling for an extra challenge as they found the game too easy. Go play Thor's standard deck solo. You won't be disappointed.
Anyway, I coupled him to the justice aspect just now and played a few games vs Rhino & Klaw. Went a lot better. Still needed the set up time and so on, but justice can simply give you the time needed. So for anyone who struggles, and wants to play true solo, I can recommend justice.
Going to try him 2H solo next. Think I'll pair Thor/Aggro with She-Hulk/Justice.