It isn't so much about the payload of the DNS requests, but about the content that would have been loaded if the DNS request hadn't been blocked.
If you load a page that has 100kB of useful information, but 1MB of banner ads and trackers ... you've blocked a lot more than 66%. But if you block 1MB of banner ads on a page that hosts a 200MB video, you've blocked a lot less.
Also a 66% blocked percentage seems very high. I have installed pihole on 2 networks, and I'm seeing 1.7% on my own network, but I do run uBlock on almost everything which catches most stuff before it reaches the pihole, and 25% on the other network.
Raspberry Pies (is that how you pluralize it?), and especially their SD cards are not the most reliable pieces of hardware. I've already had a few die on me.
As for how annoying outages are, I guess that depends on how many people and services you have on your network relying on a functioning DNS. I am running two pihole instances on separate hardware in a keepalived virtual IP setup, with a replicated configuration. Sounds complicated, but it's really easy.
It's just nice to be able to reboot or perform maintenance on my pihole knowing it won't impact DNS, and not having to worry about interrupting my girlfriend streaming her Netflix series or whatever. For example, just a couple of weeks ago I converted my bare-metal pihole installation to a dockerized one, which was a couple of hours of work, without any DNS downtime at all.