All of the above.
Intake restrictions will munt top end power. Exhaust restrictions will too. Timing/spark/lack of advance will do the same (stator, cdi, coil, plug and/or cap). Fuel starvation can show up under increased demand of extended throttle.
Powervalve actuation? Is it opening fully?
You've changed the carb so unlikely that.
Given you have 2 other bikes to borrow parts from, I would be working down that path. Start simple..
Confirm that the intake and exhaust is clear. Repack the muff. Double check earth/grounding points. Trim back some of the spark plug lead where it joins the cap (should be able to find resistance specs for this if you'd rather just probe first). Then swap out bits to check off list.
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