Is this a “new to you” boat that you just realized is working this way?
OR
Is this a boat/motor that had been operating fine since 2017 and then just started running this way?
If new to you, then:
Prop standard. Got up to 4500.
There really isn’t any such thing as a standard prop. Variance across the board. And with dealers rigging them up, different dealers will use a multitude of different props at times on the same motors and boats.
Do you know specific brand, diameter and pitch size of your prop? Without knowing more to my questions above, this is where I would be looking at this point.
Prop is particularly important as you are not in the rpm range at WOT, which should be 5000-6000 at WOT, not 4500. You should be closer to 6k with it on a light load solo.
Also, how fast were you going at 4500rpms when at WOT?
Finally, for the moment, what hole is the motor mounted in? where is the cavitation plate in the water when at WOT?
I don’t see too low of a motor mount being the sole issue, but perhaps it could be playing off something else, so checking might also be worthwhile.
If the motor checked out by a certified Yamaha mechanic, my prop would be my first go to item.
