I don't own one yet, but your reply "I don't like this" seems subjective. Or nostalgic.
I still didn't found a reason for why it would be worse or wrong to build gains to have some kind of synchronization between them.
It is subjective, indeed.
Now, to explain a bit:
You may achieve such a concentric pot in 2 ways: with or without mechanical link between the 2 channels.
My integrated Amp (a venerable Pioneer A400X) has some kind of friction between the channels.
The good think is that you may easily turn the 2 together.
The drawback is that to change balance, you need to use your 2 hands, to fight the friction. Accurate setting is therefore not easy.
Some have no manual friction (was frequently found on cassette recorders, as you show in your photos). Then, the issue is that it's too easy to accidentally change the balance.
On top of it, and whatever the mechanical option, those pots are not linear, of course, so when you modify the volume, you also somehow modify the balance, since each pot slope may be slightly different, depending on the setting.
I told you: I don't like this.
It's unpractical for home use.
Don't even think about asking a pro to use this.