No way Benning is scratched for Persson. Benning is +9 and the PK is excellent, it's fair to say he's killing it in the minutes he's playing. +/- isn't everything but that's eye popping. He's a productive player who consistently outscores in 3rd pairing minutes, that's a stability any coach is going to value.
This fanbase really underrates him, he's a 25 year old two way dman who just a the very end of last year eclipsed 200 games. It's very likely Benning is just now putting it all together , most guys don't blow the doors off but rather come along slowly. With 200+ games now and at 25 he's a legit veteran NHL dman, not an unknown like Persson and not a fringe player.
I like Persson and am hopeful that his upside is better than Benning's, but him reaching an upside of that level is very unlikely this season as he's learning NA and to a lesser extent Pro Hockey. This is a guy who came out of nowhere to play in the SHL let alone the NHL, he's still got a lot of lessons to learn, lessons Benning had learned over the last 3 seasons. Coaches won't ignore the details fans ignore, and they'll take the safer bet almost every night.