Sean and TLM are in the wrong here with their comments regarding indoor vs outdoor court surfaces. Coming from a former D3 #1 singles and NTRP 5.0, I'd say it makes a pretty big difference.
There's two big ways it makes a difference:
1) The first difference is the getting used to the surface difference. If you haven't played indoors in over a year it can take a few sessions to get up to speed. The lighting is a little bit of a factor but the court speed is the biggest. Flat shots can skid on surfaces that are fast enough. Having played exclusively outdoors during covid and only just a few days ago playing indoors, my buddy who I regularly beat handily lit me up in a set because he hits flatter than I do and his serve is more of a weapon. That means I had a more difficult time adjusting to his shots because they're more forcing than mine thereby screwing up my timing.
2) That brings me to point #2. The gamestyle difference. As more of a grinder myself with heavy topspin groundstrokes, but without a big serve, I have found my biggest and best wins have come from outdoor matches. I've also done very well indoors but theres a clear advantage to certain styles on indoor vs outdoor. MEP looks to be someone who greatly benefits from hot, slow outdoor conditions. His natural gamestyle is a terrible match for fast indoor courts.
Having spent way too much time watching, reading and observing all this, I believe Ben/GSG to be a mid 4.5 player. Others have posted (but I have not seen) that he lost in 3 sets against Topher. Sansait on his channel has said that Topher is around a mid 4.5 and a ringer at 4.0 in Sansait's match against Topher.
Sean sounds like he could be a high 4.0 - low 4.5 player. It would be interesting to see
@schmke estimate the dynamic rating score for Ben with his scoreline against Sean based on a high 4.0 dynamic rating. I'm guessing low 4.5 but could be mid 4.5 scoreline.