AirPods losing significant volume
If you are close to an Apple store, I would take them in for a factory reset / genius bar. See if they have any suggestions on monitoring. Unless you could use an otoscope or camera to show the ports clogged with ear wax - the total sound pressure can't be affected by some minor amount of cruft.

Also - in that setting you can close your eyes and have the tehnician move the balance and you can tell them when to stop the pan. If you're accurately hearing the sound output, it should be clear to everyone that you're carefully calibrated your ears and you are getting a different stereo mix when you use the same iPhone with wired headset and AirPods.

At that point, I would expect them to offer a full reset procedure and then a replacement set to be sure yours are not defective. At that point, once they are sure you're not getting proper volume, they might want to do an engineering capture / get you brand new set and/or refund your money.

I don't doubt you're getting poor volume and if you can get the support staff on your side - they might even fix the bug for us all. Sorry it's on you to prove it's hardware - but I had to go in to learn the reset procedure and a factory reset on AirPods was something you want on the service record if you want to get a paid swap / refund since it did solve volume and sound quality issues for me on one pair of AirPods.

Since I do live close to stores, I wouldn't do any cleaning other than what Apple says - and I request staff to instruct me how to clean it - possibly pointing out the cleaning KB and I'll review with them what force is safe from canned air, vacuum, etc... I wouldn't even go down the path of "suck on it” since the force from the suction could probably unhinge / break many headphone speakers unless they were internally vented in a very clever manner. (AirPods may in fact be, but I'm sticking with Apple on how to clean / maintain these.)