As a pihole alternative, I highly recommend using dnscrypt-proxy. It can provide the same system/network level DNS ad blocking but it also ensures all your outgoing queries are encrypted and spread across different resolvers so no one can use your DNS activity to profile you. I also find the blocking/forwarding rules are more powerful than pihole’s.
That said, pihole or any DNS level blocking is pretty weak compared to what uBlock Origin and provide. Like a parent commenter said, it doesn’t prevent you from seeing the google ads, it just keeps the links from working. Most big sites know not to make their ads so easily blocked.
You could send your DNS queries over a VPN to your home network... but that’s pretty roundabout and will have a big performance hit. Instead you can just run a pihole-like DNS resolver on iOS directly. I like DNSCloak, which just runs dnscrypt-proxy under the hood.
That said, pihole or any DNS level blocking is pretty weak compared to what uBlock Origin and provide. Like a parent commenter said, it doesn’t prevent you from seeing the google ads, it just keeps the links from working. Most big sites know not to make their ads so easily blocked.