So time may tell but for now Calvin just seems horrifically underpowered. The idea is cool - you can happily fail early scenarios to gain trauma which increases his skills which means you can spend those scenarios trying to grind XP instead of making progress - but the payoff really isn’t there to make up for him having such awful base stats.
Let’s compare him to Mark Harrigan, another investigator who uses something bad happening to him (taking damage) to boost his skills. Using Sophie he can boost any skill by 2 for a relatively low cost of taking one damage. Sure, this doesn’t apply throughout the whole game like Calvin’s ability, but Mark easily makes up for this by a) having good stats to begin with, b) being able to boost a stat more than once for a critical test and c) being able to heal the damage to get further uses of his ability. Calvin has awful stats unless he is close to death, cannot naturally boost his base skills above 5, and gets weaker if you heal damage or trauma from him. Mark even benefits from taking damage whilst Calvin gets nothing other than approaching having a decent stat value.
Calvin’s weaknesses are pretty glaring. He is awful at the beginning of a campaign (or any time he has less than 3 damage/horror on him) as he can’t do anything effectively. With 0 in everything he has almost no hope at fighting or evading enemies and he can really only discover clues by using Flashlight to make locations 0 shroud or via events. He can use enemies that deal damage to boost his physical skills, but when stuck with an enemy that only deals horror he is going to be in trouble. Even 2 is a bad number to have in a skill and 3 is still poor, so he really needs at least one other investigator to kill enemies that he cannot handle early and another one to discover clues. However, this goes against his desire to fail scenarios in order to gain additional trauma as the other investigators are not likely to want this to happen, leaving him in an awkward position early in the campaign. Once he gets some trauma he starts to become okay, but then a lot of his deck needs to be devoted to keeping him alive and becoming merely ‘okay’ is not worth the annoyance of being useless for a long time.
So all in all he is definitely interesting, but I can’t really see him being anything other than awful unless some amazing combo comes out that only he can use.