"Superman allows himself to be hit in order to get some measure
of an opponent's power levels. "

That certainly contradicts the Superman I grew up on. He might allow himself to get hit by common thugs if he needs to get the point across that he's invulnerable, but hitting him is like punching solid steel. A hard punch would crush the bones in his opponent's hand if he was just a regular guy.

The Superman I knew would go out of his way to stop people from getting hurt, even criminals. He pulled his punches, he kept track of every bullet bouncing off his chest and he would quickly roll with a punch sometimes to prevent the other guy from getting hurt (especially as Clark Kent).

And letting himself get hit to gauge someone's strength? If the other guy was strong enough to punch him through a building, that would be putting bystanders at risk.

If he was sure that the other guys couldn't knock him off his feet, he might let them hit him so they'd wear themselves out (rope-a-dope-style), but intentionally taking a hit for other reasons? No. Doesn't make sense.

It's often been portrayed as a failing in Superman's enemies (and especially in Luthor) that they view him as all muscle and as somebody who rushes in, expecting his powers and invulnerability to save him). That was a recurring motif from the '50s to now. And the really good writers (no matter how corny the stories may seem to modern readers) made a point of it that a lot of the time Superman defeated his enemies not by being stronger than them, but by being smarter.

I'm not saying that he had a higher IQ than Luthor, Brainiac et al. or even a comparable level of super-intelligence, but he managed to identify their weaknesses and outwit them. Often precisely because they underestimated him.

And a Superman whose idea of testing his opponent is to let him have the first punch, seems both more macho and more of a musclehead than I'm used to. It seems more like Luthor's view of him has been embraced by the writers.

Maybe that's a bit harsh, maybe it's part of a larger idea of Superman where it makes sense that he would just let people punch him without having an idea about how strong they are. But my gut reaction is "nope". It just doesn't feel right.

"(It is more likely he lets himself get hit, like by the hammer, so nothing else gets hits because he dodged it.)"

That, I agree with. He might let himself get hit to protect somebody else. It's just the idea of letting himself get hit to get the measure of somebody else's strength that doesn't seem right.

If somebody lands a punch on Superman that sends him flying, it's because  this other guy was too fast, sucker-punched him or was much stronger than expected.

Was that with the roll of  12 or 16 sided dice?