Most dryers should have tumbling rates that (should) do exactly that 11/12 to 4/5 tumbling.
However, its hard to get the proper speed for any load.
You see, most dryer motors are not speed controlled per se. They are designed to give a certain output speed at a certain line frequency. Saves a whole lot on electronics (whole lot in developer standards, aka now where near 50 bucks probably). And further, you can probably optimise the motor to run at max efficency at that certain Hz number.
Onwards, most fabrics don't need special treatment tumbling wise to survive a drying in a tumbler (more on that later).
Bur, drying is a pretty random thing. Tumbling patterns of loads are incredibly complex. A load can be the exact same and tumble 100% differently. Some loads are lighter, thus not sticking to the drum as easy, others have items that are somewhat less airy, thus getting kind of "blown up".
So, manufacturers take an average speed to get most loads tumbling as good as possible.
Now, some could say "Why don't they add a sensing feature?"
Well, some did, kind of. I know that Miele and Electrolux both have sensing procedures, not for drum speed, but for reversing.
A load that becomes tangeled either rolls or drops as a bunch. No matter which configuration, anytime they hit a baffle, the motor has a sudden load peak, thus, if one would plot the power draw over time, there would be serious spikes noticeable. The electronic monitors those spikes and, if they get to big, they trigger a reversing cycle.
Now, why is sensing for speed not done? Well, my guess would be the randomnes of loads.
To put it extreme: You could have 100 pairs of thin socks in your dryer. Per se, they are light and tumble well. But a simple weight sensing cycle would say "Heavy load, slow down!". Thus, they'd roll and not dry well. On a mixed load, depending on sensing, the load would seperate in a bunch of clothing sticking on the wall and the rest tumbling.
Further, a 3D-sensor used for example on Panasonic washers (which watches the drum for sudden movement during wash in correlation to motor load) can't apply neither as the drum is rigged mounted.
So, sensing would most likely only lead to even more disturbance (at least, by my logic).
Anyway, some try to get arround this. Newest example in the EU: WPs hollow lifters, guiding air from the back of the drum through the lifters out of holes into the drum in a 90° angle to the regular air flow.
Sidenote: Electroluxes heatpump dryers here in Europe use actually up to 2 Inverters. One controlls the heatpump power on the A+++ models, the other drum speed.
Why? They usually stick to the same regime of speeds as a normal dryer. But there are exceptions:
On a night mode (only TOL models), they slow down to reduce noise.
During initial sensing, they slow down to max the sensor contact.
The wool cycle speeds the drum up to get the drying flat effect by fixing items to the wall.
The silk cycle tumbles verry slowly to reduce creases and wear.
There are probaly more varriants, but these are the few I know for sure.
