You REALLY make me think, George. I've been doing these accordion playing things you describe automatically for years, and now you're making me look at all the little components of playing (that we do without thinking) as individual tasks and it blows my mind!
I think you're spot-on with the concept that rhythm comes FIRSTLY from the right hand melody. I could easily visualise playing for dancers only using my right hand, and the rhythm and lift would still be there. In fact, in a band setup, the left reeds of the accordion are rarely heard at all unless the balance of sound is wrong. Originally, fiddles or pipes would have been the only or lead instrument - melody only of course like our right hand - and they had no lack of lift. Not being a fiddler, I assume they achieve the lift and variation in volume by bow action being harder or softer?
How on earth does a piper achieve lift? The bellows (bag) pressure MUST be constant or all the reeds and drones go wrong. Must be adjusting the length of the notes by making them shorter or longer? Do we have a piper on the forum who can tell us?
What we do with our bellows, and I include all of us from the newest player to the virtuosos, is control the volume. That SOUNDS simple - squeeze harder and it gets louder. BUT, and it's a HUGE 'but', even that is not as simple as it sounds.
To illustrate what I mean, if you imagine that an accordion could be 'powered' by an electric pump giving constant air pressure, and had no bellows. It would be like a harmonium or pipe organ turned on its side.
If we held down one note, there would be 'x' volume on that note - constant and unvarying. If we then hold down two notes, since the air pressure is still exactly the same coming from the pump, the air is now being divided between two notes, half to each. Would that mean the total volume would be the same, but the volume of each of the two notes would be halved?
Then add a three reed bass chord with the left hand - we now have five reeds using the same total air supply. Same total volume and 1/5th volume on each of the individual notes?
As if that wasn't bad enough, small reeds (high pitched) need far less air to make them sound than big bass reeds, and that will constantly change as we go up and down the keyboard. Factor in the one to four sets of reeds we happen to be using on the RHS and the same on the bass side, add the fact that we DON'T want the volume to be static, we want it to rise and fall to create this mystical 'lift' and the whole thing is a nightmare of complications - yet a child can do it!
I think my message to beginners would be 'If you can play a single, simple tune using both hands, you are doing something that less than one in 100,000 of the population can do - be PROUD!'