Why don't you go look at his analytics last year? When he wasn't getting baby minutes. Spoiler alert, they were garbage.
Oh wow, the difference of a 0.03 PPG. That's such a massive offensive difference, like you said, "Riikola provides way more offense". You are aware that the difference between the two is the equivalent of 2.5 points over an entire season? Riikola's pace over Johnson's games played is 13 points. We're talking about a 2 point difference here.
The only person "so wrong" here is you. Riikola is a bad defenseman that's either going to be out of the NHL or a #7 on a different team next year. He's an offensive defenseman that can't produce and regularly makes stupid as hell defensive decisions. He has the same hockey IQ as Johnson, he just skates better and shoots harder than him. The only person wrong here is you, because you think a crappy fringe NHL/AHL defenseman is good.
Or maybe that both are such bad options that playing Ruh on his off-side is more attractive than playing either of them.