Those are great troubleshooting tools or videos. Definitely there is good spark on #1 and definitely it is not firing as indicated with no change in engine tune or rpm when plug wire is pulled. And you said you have 125 PSI compression on each of the three cylinders. And then when you sprayed fuel mixture directly into #1 cylinder while engine is idling, there was no change in rpm either. And you have also confirmed the reeds are in perfect conditions. With these diagnosis, the only possible cause of #1 cylinder not firing is because it is not sucking fuel-air from the carbs but rather more likely sucking air from leaks rather than through the carb.
It is really very hard to test where the leak is coming from and it is so badly that not enough fuel gets into the cylinder. But you can always test if fuel is actually getting into the cylinder by doing the wet test with a napkin. I understand the spray bottle test is supposed to have test for this but that is mostly for the carb section of the fuel-air mix to enter the intake but not the crankcase and eventually the cylinder.
Wet test by balling a white napkin, remove the plug on #1 (activate the kill switch so motor does not start) and place the ball of napkin in front of the plug hole and crank the motor for about 3~5 revolutions. The napkin needs to be really close to the plug hole almost plugging it but you want all the air to escape and just catch the fuel with the napkin. Fuel in the napkin will be indicated by yellowish stain. If there is no indication of fuel going into the cylinder, have a second person spray fuel oil mix directly into the carb while cranking it over and holding the napkin in front of the carb at the same time. If there is no indication of fuel still, it tells you the crankcase on #1 cylinder is sucking air from the outside rather than through the carb.
However, if there is an indication the cylinder is flooding (too much fuel wetting on the napkin), maybe you can try swapping carbs as previously suggested.
Sources of leaks that can cause reduced fuel mix going into the cylinders are the upper crankcase seal, fuel recirc system or fuel drain covers.
