I'd instantly suspect the compression gauge quality if I got all numbers like that, they just don't really do it unless the engine is under 5000 miles. I've seen defects at 2000. But whatever. If it IS the compression you will not get the issue to stop with ignition. BTDT.
The black rings you talk about have nothing to do with slide 'sealing', the slides seal at the OD of the slide top biggest diameter, the grooves cut into it do it. The seal there is differential air, and why the slides on those are so much more sensitive to engine condition that rubber diaphragm sealed ones are. The black rings are wide open bumper stops. They change color (thickness) depending on the carb bore to match wide open setting on the different carbs (28,30,32,33).
If nothing is messed with on the bike including the airbox then the slides only improve opening with engine condition, the engine MUST be sound and sealed tight to pull them open, it cannot be over-emphasized. Engine draw is what yanks them open all the way. Messing with stock airbox can kill that as well. Gone to use pods I guarantee the slides will not open fully. I take note of no word on that, a common messup that puts people where you are now. The rolling off of throttle to run higher rpm screams it.
It COULD possibly be the plugs but it would be the odd bird to do so, they have to be pretty bad to do it. On other engine types I always go to plugs first but not on these. Far too many never ever touched the valves at all and then throw $$$$ at why they won't pull out to 9500 and wasted. Most engines the valves get looser but on these they tighten up generally with use and based on the whopping cam looseness and crap valves that were only barely surface hardened at all. They then recede into head to leak with any use and then the engine misses both due to compression leak and slides too rich from not opening up. They if not adjusted then burn exhausts at the drop of a hat. The lead indicator of that is the top rpm not pulling out, it will get lower and lower. How most of them die. Honda sped that up by saying in the service manual that the valves set at .002"-.004", and many of them burn valves at .002", been there myself. The clearance has to be opened up to 4-6 to make them live. I've seen brand new ones set at .003" be at .001" by the 600 mile initial new bike check and those already burning. Why the Honda spec sucks.