Revving in neutral and then from idle to wide open only tells one just so much, we used to call that a speed tune when a guy is hoping something blocking his carb will dislodge itself. One needs to study what is going on with an engine at all operating RPM not just idle to wide open especially considering the carbs have three fuel circuits being the idle, main and secondary main which are the slides. From the one second clip that I saw, it got down to idle speed.

I like to see a problem engine idle for a bit, then a slow roll on of throttle, slow roll off, quick roll off, a quicker acceleration and so on listening to the engine for backfires, surges, uneven running, intake noises, etc. all part of diagnosing. The engine then is running on just idle and main circuits (no slide action), slides only open and provide more fuel under moderate to heavy engine load. With an engine stationary I never rev up to more than 4000RPM or so and then just briefly. Drive it on the road like grandpa would not going over 2000-2500RPM and on level ground through all the gears. This operating condition will not call the slides into action which you will watch them stay closed. How does it drive then? Slow it down to 1000RPM in fifth gear then first time very lightly and next time heavy accelerate, it should pull up to speed, what happens? On a problem 1500 I can spend 2-3hrs diagnosing plus plastic removal time which system is at fault from compression checks, engine mechanical defects, fuel delivery, carb, spark, emission devices, electrical, road testing, spark plug condition etc. Your eyes and ears are foremost in gathering clues. During a normal driving road test what RPM does the problem start, what RPM does it go away. Does it get progressively worse with RPM. No need to race track it at all. The faster you ride it the less time you have to make observations. Your wide open problems are probably there in some subtle form during normal riding. Verify and verify again.
Along with carb problems the 1500 can have shot air, vacuum hose misrouting, air jet solenoid, AIR injection problems to name a few which affect the mixture entering engine. The GW 1500 is one of the most difficult to diagnose and repair bikes ever made.

We will continue to plod forward on the assumption it is lean running because 90% of the time that is the culprit.