The number of reservations per ride was not higher with FP+, by all accounts. They just had more attractions, like Fantasmic, Illuminations, parades, meet & greets, etc., which provided a fair amount of extra capacity. All the rides and shows were running as well.
On super busy days (like today), all the FP+ rides for the headliners were sold out way in advance. Multiple insiders have said that with classic FP, FP+ and now
Genie+ the most common ratio used by most of the headliner rides is 80% FP (LL), 20% standby.
It's barely possible that some of the rides are not running at full capacity because of staffing issues, but I think it's more likely that there are several big people eaters at some of the parks that are either gone or not operational. Indiana Jones alone would suck up thousands of guests for a long show. Voyage of the Little Mermaid is a decent sized theater. Hollywood Studios just needs more rides and needs to have all the shows back open.