Monster Girl was also tearing apart 2.0 drones which Viltrumite War level Mark couldn't one-shot, even when in space. Not only that, but we know Monster girl's monster form strength is inversely proportional to her appeared age (handbook + Kirkman). Kirkman said older-looking Amanda near the end of her story had a monster form which should've looked around the size of a large bodybuilder, but it wasn't conveyed properly. With this in mind, it'd mean Beginning of series Monster girl>>End of series Monster girl~EoS pre-500 year Mark (drones bled his mouth in the final arc)>Viltrumite War Mark, Nolan, etc. Comic has plenty of iffy scaling moments. Unless you wanna buy Monster girl is small planetary off the bat and gaps 90% of Viltrumites.
I honestly don't see any indication of pain anywhere there. Usually blood is an indicator of even the slightest bit of damage, but discounting that it mostly just seems like Mark struggling to immediately break the Mauler's grip - he was still feeling relatively groggy from the paralyser gun so it seemed like his muscles were numb and unexertive in those moments. I also think that was the reason why he dozed off after the nuke (despite no physical damage being received) and partially why he initally struggled to keep up with Oliver, despite it being established earlier that he's MUCH faster.
Tbh, Steven Yeun is a fairly expressive VA. He makes sounds for Mark, that'd be interpreted as struggle, on occasions where he's doing the most mundane activity. Example off the top of my head is when
Mark play-fights the headlamp thingy on the Atlantis monster's head, thinking it was the tiny fish he was supposed to face in trial-by-combat. It was jokingly, but he made it sound like somewhat of a struggle when he hugged it. This is only 1 minor example - I got that from Yeun a lot. His expressiveness is what makes him such a good VA. Simmons sometimes does similar stuff, but more of a
roar type noise. Most recently made a
similar type of noise in the S3 flashback.
This is one part I don't find inconsistent at all. I've seen a lot of people mention it already. Nolan didn't get "dogged on". He was bombarded with a bunch after already getting slowed by a ton of shit, like the orbital laser, which at least hurt him. After he locked in he pretty much just tore them apart with the same ease Mark did. No physical damage inflicted on him - they couldn't even make him bleed after biting his noise and his skin and actually pulling out with the bite. A barrage of punches from those things made some pretty hefty bruises on Mark's back. I wouldn't say minor discrepancies in some fights relative to others is a genuine claim to "weak writing" or counted as an instance of one. The writing in the show for what matters is great, and minor power level shit is passable. Viltrumites above all will always be kept at least somewhat consistent.