The issue is the mix. The problem would all but dissappear if Riviera had the bypass.The Skyliner's "slow" problem is that they didn't build a physical needs bypass at Riviera. Every EV and person/group going on or off at Riviera that needs more time slows the whole line down, and sometimes stops it completely.
If you have special needs pull-offs at every station, it can be pretty speedy. But don't count on speeds over 15 mph (WDW's Skyliner's top speed is 11.2 mph (5 meters/sec).
Specific gondola cabins are configured to bypass. I'm thinking every 12th, not sure of the exact number. Riviera would work better if the line could be slowed or stopped and then 3 or 4 scooters loaded at once. That can't be done, the scooters designated to bypass have to be spaced out.