A couple examples of D-II schools upending D-I schools. 2 years ago, Grand Canyon University was #20 D-II team and they beat Northern Arizona 5-2 (All matches were completed and final score was 6-3). Last season GCU played Cal Poly, which was ranked around #50 and GCU lost 5-1 (7-2) Most of the matches were very competitive, but Cal Poly was definitely the better team.
Additionally, 2 years ago Hawaii Pacific (a top 10 D-II school) walloped Air Force.
The #1 D-II team in the country (Armstrong Athletic) often plays and badly beats some D-I teams. If fact, I'd love to see the results between AA and perhaps a D-I school ranked around #30.
As for UTSA "easily" beating a top D-II team, the singles were all straight set wins, however there were several close sets and UTSA did lose the doubles point. Perhaps "easily" is a bit of an exaggeration.