I've found much of the same. Though sometimes one of the devices on my network seems to favor the second server for a while, and one time when the two DNS serve

I've found much of the same. Though sometimes one of the devices on my network seems to favor the second server for a while, and one time when the two DNS servers were out of sync I couldn't get that conputer to resolve any addresses that weren't synchronized without a reboot. I think the moral is not that pi-hole is bad or risky as OP implies... it's that DNS is never simple and running your own with proper redundancy can sometimes be tricky.