A typical operating system should not have stability issues just because of badly prioritized interrupts. You may have severe performance issues, sure, but if you're crashing because someone didn't handle an interrupt in time, someone designed something wrong. Maybe it's not software's fault and some hard engineer made bad choices, but this is generally not true today since no mass market OS actually guarantees interrupt latency.
That’s a pretty bad idea in general. Handling priorities properly is absolutely essential for the stability of a system. I’m not familiar with Amiga, but systems weren’t known for their stability back then. Whole OS crashes were much much more common back then.