Percentage error seems to be clearly better than absolute error.
As for adding other terms (ie. not just P), I do think the benefits of other terms need to be weighed against the unknown-unknown risks of creating a more complicated system that is more vulnerable to attack. A big difference between traditional PID controller theory and the crypto world is that in the crypto world, there will be actors trying to manipulate the outcome. The IMO quite small gains of ensuring that target price more closely follows market price instead of drifting off by 1-2% should be weighed against the greater risks of attack that come from more complexity. The best argument for adding an I term would be if you discover a reason why adding it would lead to less risk of attack. I’m sure an experiment of running the I term live will teach us things, but I don’t think that it would give sufficient information to answer that question, as attacks often don’t come until years into the system’s evolution.