Pau, is maybe the most underappreciated Spurs player. Last season, he was one of the best in the league at protecting the rim. He also shot the 3 very well. His defensive advanced stats were as good as LaMarcus's, and I know more fans will find hard to believe. Regarding his offensive struggles, you are absolutely correct. I could be wrong, but I think it's because of that should injury he had that never really healed which was a result of him playing longer minutes out of neccesity as Kawhi, Rudy, Tony, all missed time due to injuries.
Hopefully, if he is healthier and plays less, his offensive production will go up.