It's not that MMA striking is overrated, it's just very different. In MMA, you're worrying about different things. Strikes come from different angles because you're taking into account kicks, takedowns, sweeps etc etc. You look at a top level striker in MMA (someone like Stephen Thompson, for example), and it's pure poetry. But it's not boxing. It's hard to erase a career's-worth of muscle memory. I train in Karate myself, which is predominantly punches & kicks - but the way you throw & set up punches is very different to the way a boxer would.
As has been said many times, stick a boxer in a cage with an MMA fighter under MMA rules and I'd be surprised if they get past the first round once they start getting their legs kicked from underneath then. It's two completely different worlds. Not to say one is better than the other, just different.