Yes, Im not sure what is 'career defining' if Loki isn't. He's signed up to two series of it, when Wanda Vision and CA v WS only got greenlit for 1 season each, so he's hardly reluctant. Re the career thing. He's working, he has a big role in Marvel things. If he's boring, as you say, just own it, get on with your life, don't do any more showmances and do your job, which it seems like he's doing. He doesn't owe his fans his private life. I respect actors much more if they don't do social media or have PR telling them to do stupid things all the time. The 'Oh he's so dedicated to his career he hasn't got time for a girlfriend' sounds like the same stuff that's on the Henry Cavill thread but Cavill sounds like an idiot for responding to fan gossip about his new girlfriend. It makes him sound desperate for people he doesnt know to believe him. At least TH isnt doing that!
The thing with the paps is, that they very often hang out in Central London or work on tip offs. If celebs are papped, its normally because someone has tipped them off, or there is a news story about them. A lot of the time it's one of the couple. Benedict Cumberbatch lives in Hampstead (or did a few years ago anyway) Celeb central but he is hardly ever papped with his wife and children because no one called them and presumably they don't go to celeb hangouts in Central London. Some couples are papped all the time, even when there is no reason for paps to be outside their house, because either they cant trust their neighbours or they themselves have called the paps.