You are the most qualified based on that, and I observed a few things that I feel tend to support GSG in this matchup. Against Max, you tended to "feed the animal" so to speak, and give him quite a few balls that didn't challenge his movement and were high in his strike zone. Max seems to handle the chest high ball exceptionally well. Now I only watched about half of that one match of Max, but he didn't seem near as strong in the other areas of his game. WHile his serve was pretty energetic, I don't see it giving GSG too much problem and instead of getting something chest high past the svc line that Max seems to favor, I expect GSG would give him a steady diet of soft low skidding slices on a diagonal path, that don't work into the better part of what I saw Max do in your vid. Bringing him in on a diagonal would tend to play into GSG's strengths of slicing away, passing deeper CC, as well as lobbing just over his reach.
GSG's serve is likely deceptively quick, but more important, it stays sort of low and short. This greatly limits the power for doing damage or the rtn putaway and will challenge your patience. I think top players would generate moderate good power and challenge him at his feet or cross court, looking to finish on the 2nd look they get. They could also hit some good drop shots that would be tough even though GSG is often following is serve. For most players, this is a tall order to execute well against GSG's short low slice serve as he moves in.
Not picking a winner, but think GSG's game creates far more demanding court positions than people realize and positions that most have not used all that often. Max does play a lot of doubles I think and that would be a big plus here. I'm sure I missed it, but I didn't see any comments on GSG's near total lack of UEs....which is a major issue against any rec player.
