Timemaster blade belt wear

I have a 2016 Timemaster. The original v-belt that drives the blade lasted almost a year before it started to slip. I took the cover off and the belt looked glazed and a little worn (not cracks but width was worn) so i replaced it. I let a friend use it on a large suburban lot with tall grass and ...that belt now needs replacing about 3-4 months later. (I'm assuming that's whats wrong from his description of "the blade never seems to get up to speed"). When I replaced it last time I noticed that the tensioner, ie the pulley that the blade engaging (operator position) lever moves up to tighten that belt and start the blade has a little black plastic/nylon wedge that rests on the keyed belt (the long belt that connects the two blades and that the v belt drives) when the tensioner isn't engaging the vbelt.
1- Is that normal? I'm sure the plastic is slippery but it seems like that will wear the back side of that keyed belt.
2- How long should one of these vbelts run? A year doesn't seem like a long time, and even though it was used on tall grass (dry, which isn't the norm here in the north west) 2-3 months is way less.

Timemaster blade belt wear