[pkal]

Some sites like Anna's Archive have .onion site for the Tor network, and others do not. Is there a considerable downside (DDOS?) to providing access to their site by those means?

[flipped]

I have seen Tor network take a hit when there's fight between darknet marketplaces. It's certainly an issue.

[m00dy]

not anymore. Most recent onion sites have enabled proof-of-work mechanism in place, so DDoS attacks are now expensive to carry out.