Greul has the experience going on and weighs in a lot of matches at this level, lets not forget the guy knows what it is to win on bigger stages and has been a solid top 100 player just a couple of years ago! Didn't get to see both of Pella's matches against him but no way he's been shit lately, this season has been awesome for him, hoping for the big breakthrough next year, and didn't perfom bad at all in his past tournaments.
Greul is past it though, time for him to retire, like you said he was top 100 2 years ago
. Pella has been kinda crappy lately.