The Padauk FPPA chips are probably a bit better at bitbanging strange protocols than any ARM, but not in the same class as the Pi's PIO.
• decrement the X or Y register;
• conditionally jump to a specified target address if it was nonzero;
• otherwise, jump (by "wrapping") to some other specified target address, usually an outer infinite loop;
• change the state of four or less GPIO pins to immediate constants;
• delay 1–15 clock cycles.
Arguably IN can compete here, replacing the first two items with:
• set one or more GPIO pins from bits shifted out of a shift register;
• conditionally "autopull" a 32-bit word from an input FIFO if the shift register is empty;
• conditionally stall the pioasm program if the FIFO is empty;
• conditionally initiate a DMA request to refill the FIFO if it's not full.
The OUT instruction has similar "autopush" capabilities.
Most of these are somewhat independent choices, but if you don't pull from the FIFO you won't have the other effects, and several of the options are state-machine-wide.
https://magazine.raspberrypi.com/articles/what-is-programmab...
The microcontroller has additional cores called state machines in the PIOs that are specifically designed for bit banging and have their own custom ISA that reportedly only has 9 instructions.