That's a good observation, which I've had in mind while designing the prototype.
I've considered alternative input methods; if I were to continue this prototype, I'd firstly test a mobile implementation, where the input system involves swiping both thumbs up and down in place of pressing the keys while generating a similar motion.
Another alternative is adding an accessibility / easy mode where less keys are required, with each key controlling more than one tentacle.
Anyways, thanks a lot for the feedback!