Do people really think the Apollo computer is more powerful? And have any evidence? I'd be surprised if you can get a microcontroller with as little processing power these days.
Music cards use dedicated chips, they are not general purpose, and they don’t really do much computation aside from a few counters. AFAIK.
Now, in DIY tutorials they show microcontrollers, because they are easier to obtain, but it doesn’t mean that they are used in the commercial products.
The cheapest, smallest (15s storage) "chip corder" (which is what these cards use) has GPIO, SPI, the ability to trigger different messages etc. There's no way this is under 12,000 transistors![2]
[1] https://en.wikipedia.org/wiki/Transistor_count#Transistor_co...
[2] https://www.datasheets.com/en/part-details/isd2115ayyi-nuvot...
It seems likely they are using something similar. It's difficult to find a cheaper chip, broadly available chip these days.
You can find Z80 clones, but even they are generally upgraded and therefore more powerful than the Apollo computer.