TL;DR I tried to force Chromecast (and everything else) to use Pihole as DNS and misbehaving devices (like Chromecast) hammered my pihole into oblivion. I'm talking tens of thousands of requests in a very short amount of time which caused my RPI4 to stop responding to DNS requests (dashboard was still working though). See linked comment thread for details but suffice to say 4 virtual machines with pihole behind two load balancers still saw some downtime. OPNsense gateway is a much better (and safer!) fix IMO :)
All of this hardcoded DNS server BS in iot devices is a pain.