Didn't finish. Souma isn't just "grumpy". He gives the MC traumatic sounding flashbacks/makes him feel ill with his presence, he yells at the MC a lot, he physically drags the MC places against his will (This is only in the beginning of the story and does taper off in Izumi's route but I can't speak for Souma's route) Izumi's route is cute and wholesome.
I edited this because I said Souma comes across like an abuser. I did not do his route, and I still think he is terrible in the beginning. The way the MC reacts to Souma is what makes me think they had a toxic relationship. I won't say he is abusive in the story as far as I played, but the way the MC acts around him makes it seem like maybe he was. The MC has nightmares about him where he wakes in a panic, feels physically weak/drained when he sees him, flinches from his grasp and can barely look at him... Not to mention the moments where the MC says he thinks Souma looks like he's going to grab him by the collar and yell in his face, or when Souma calls the MC a coward because the MC walks away from him because he feels uncomfortable to the point he can't bear talk to him, or when Souma vaguely says "you know how I get sometimes" when referring to his anger issues, or when Souma just baselessly insults the MC and tears him down even though he can tell the MC is struggling...
Most of the glaring issues with Souma are in the beginning of the story with a few places that just need clarification later on (clarifying anger issues). Souma's set-up as a "nice guy who has anger issues" is just too strong in the "anger issues" department. A good example of making someone "too mean" is in the movie Shazam where the "school bullies" hit a kid on crutches with their car and then just start beating him up. That is not "bullying" that is a second possibly first degree felony. Bullying is wrong and harmful, yes, but attempted murder is a different level. I get that "anger issues" is vague enough to encompass many things, but Souma is still supposed to be a sympathetic character. So, the "anger issues" can't be so severe that they make him unsympathetic or a bad relationship choice for the MC.
Later in the story, Souma does appear sympathetic through his interactions with the side characters and his behavior, but this is overshadowed by his initial build up. He is fine to be frustrated or angry, but the instant he starts physically dragging the MC places and yelling insults it is over the line. The fact that they haven't spoke in 2 years and still have this terrible feeling between them that makes the MC feel ill and have night terrors is really off putting.
I feel strongly about this, because this is a common thing in dating games. I'm afraid that it encourages the thought that guys who are giving bad vibes and bad signals are secretly really nice. So, even though they yell at you and physically drag you places against your will and belittle and insult you, they are actually really caring and just misunderstood. In reality, they might be nice guys who have emotional problems that they can't deal with on their own but aren't seeking out help for (so they take it out on others). Or, even worse, they aren't nice guys at all and have issues and will abuse their partners (emotionally, physically, verbally, etc). I get that the MC knew Souma from childhood, but it has been years since they last spoke. And, at face value to the player, he is setting off red flags of being someone who is unstable and looking to get back with someone he could push around. The thought of "I'm yelling at you and doing all these things that hurt you because I care" is also dangerous.