It's true that the majority of NTRed male MCs are weak in bed (sometimes exaggerated with a micropenis and premature ejaculation, but often just average sex skills). The reason is most likely because that set up for the characters just fits the NTR themes the best.
NTR stories that stays close to Japanese NTR style generally follows the path of corruption of the pure heroine by some asshole with sexual prowess. They are usually not telling a story of an adventurous woman who wants to cheat "for the thrill," nor a scorned woman who is angry at her partner and cheats out of spite. It's specificically trying to show a loving relationship that is ruined by outside forces. It's also worth noting that the male MC isn't necessarily a "loser" just because he can't give multiple orgasms like some giga Chad (that's basically normal, and the antagonists that have unnatural sex powers are the fantastical ones). So giving this otherwise healthy, loving couple one weak point that the antagonist can tackle to corrupt the woman just seems like a natural fit. Blackmail, rape, manipulation, seduction, or anything else can get the baddie to sex the woman, but her "fall" happens because the sex is just much better. There is a reason their body falls much earlier than their willpower in most cases.
I'm curious to see what type of male MC you are looking for in an NTR game if you don't enjoy a "loser" MC. Because frankly, that's like asking for a hypermasculine Giga chad MC in a hardcore femdom game. It could be done (and could even be interesting), but it's not the natural fit, you know?
I get it, but the specific element of NTR is the feeling of jealousy. It is the feeling in your gut you get when learn the MC is being cheated on. Of course everyone seems to have an opinion on NTR... some people think that if your MC turns a LI down, if that LI then goes off and has some fun with another partner then that's NTR but that is not the original definition of NTR. So my point is, you don't have to automatically be a loser to have your wife/gf cheat on you. You could be fine in the sack, have a decent job, etc but for whatever reason, your wife cheats on you and that feeling of jelousy in your gut is NTR.
So to answer your question, I would like to see an MC who gets ticked off and maybe does something about it. There is another game, Rise of the Crime Lord, where is the MC is clearly not a loser. He pleases his wife in bed and is good at his job, but his wife can still cheat on him. Jelousy is not dependent on being a loser. Yes, the MC may be a cuck but that does not automatically make him a loser. Jelousy can happen in a variety of ways to a variety of people.
In this game, the player has 1 choice... that's it. He can tell his wife that one should throw all their values aside or never throw them aside. If the MC says never throw them aside, the game ends. I mean, what is the point of that? That is not really a choice from a player perspective. So basically, you have to play the MC as a loser who is willing to sell his soul to survive or his wife dies. That's just silly.
Anyway, I don't want to get into a debate about NTR and frankly, everyone seems to have a different opionion about what NTR actually is and whatever works for you is fine by me. But you asked me a question, and this is how I look at it. Is it right? Not for me to say, but it's how I feel.