i would encourage anyone who wants to write sparring scenes to actually spar with someone. just go for 2 minutes. that's a pretty long time, at least it feels that way. your thoughts don't drift while you're fighting, you're focusing on breathing, looking for an opening and psyching yourself up to ignore the pain and just *go* for it. you don't spar at full power usually, you go like 50% or something. you both set a limit and stay there. like a light jog vs a sprint. you won't be able to go for long if you go all out.
even if you're down at 20, 50%, you will still get hit and it will still hurt. sting, at least. if you get kicked in the stomach or dropped on the ground you might get the wind knocked out of you and be unable to naturally breathe (in which case you will gasp uselessly until you mechanically force the breathing. a fair fight will pause while you do this).
your arms and legs and body will sting where you've hit and blocked, and you'll start to favor limbs or try to avoid putting them out there. a good portion of your thoughts are, again, devoted to overriding this instinct and just pushing forward. you're also gauging what your partner is doing, how tired they look, how aggressively theyre fighting. what moves they might be pulling over and over.
fights are fast. you'll engage, disengage, and press in short bouts of several seconds. a round of combat in dnd lasting 6 seconds is about right. but in a friendly spar at least, you'll probably take some breathers between hits. step back, circle, regain a little stamina, then press again. when your opponent presses, to avoid getting hit you will usually back up. there's a lot of Trying Not To Get Hit in sparring. you probably won't have a lot of breath for conversation, sparring is A Workout.
now if youre writing superheroes, yeah theyre going to have more energy to spare and will be less bothered by pain (sometimes just by Not Getting Hit) but if theyre up against an equal or near-equal they should be similarly exerting themselves. not every hit should land, not every not every second will be a press, etc.