Check that you were using the null blocking variant. If using a nxdomain variant it applies a filter per domain. Pihole and hosts files include a massive amount of subdomains as the filtering is done at subdomain level. Using those lists with nxdomain filtering grinds your machine to a halt. In the words of the adblock developer
One major drawback of the 'null' blocking method is, that it only works per single host entry ... you can't block a whole domain (e.g. including all subdomains) with one single entry. That's may one reason why these pihole guys working with such big blocking lists.