Ok, some of us are in agreement that your rear wheel and its bearing, and gears looks and sounds normal when you turn the wheel by hand.....
So back to your original complaint of screaming engine and lower top speed and power loss:
Gease or oil on the pulleys could cause all the above. A leaking seal in the CVT or incorrectly done lube job?
Or - too light weight rollers installed could give same performance problems.
Does your expert mechanic agree with you about "screaming engine & power loss"?
Stig