If your takeaway from Game 6 is that "Gobert can't guard the perimeter", then you didn't understand what was happening.
The reason Snyder's gameplan was to keep Gobert in the paint isn't because "Gobert can't guard the perimeter". It's because none of the other four guys could prevent penetration. If Gobert isn't camped in the paint, it's a layup.
Is Gobert's value as a rim protector basically nullified against 5-out offenses? Yes. Is it fair to question whether this team can win a title paying as much as they are to Gobert, considering the league is going to keep going more and more in on 5-out lineups? Absolutely. Does Gobert deserve a ****load of blame for having several inexcusable mental lapses once we got up 25? Hell. Yes. Does he deserve criticism for being unable to punish small ball on the other side of the court? How about for not dominating the boards? **** yes.
But in this series, Gobert's defense wasn't the liability. Everybody else's was.