It wasn't an investigation of himself, though that would have been worse. It was an investigation of Flynn's ties to Russia, a country that Trump believes hacked into the election that got him elected president. And Trump asked Comey to stop the investigation. Then fired him when he didn't.
But no, why would that concern you? You want even more executive overreach than even Obama undertook. Let's keep the presidential overreach circle jerk going.
I don't think presidents asking FBI directors to stop ongoing investigations is a good thing. But that's me. You don't like an independent FBI. That's just like, your opinion, man.