Flicker has a relatively low free tier and is targeted at people who are amature or professional photographers, ie people who can afford at least 2k of entry gear.
Tumblr has no paid tier and is targeted at (or mostly used by) teens and early twenty-somethings.
So I would question any direct comparision between the two.
Flickr killed Pro several years ago, removed restrictions on the Free tier, offered paid options to go ad-free or add a second TB of storage, then later killed those options and brought back Pro as stats and no ads.
Flickr's free tier is no longer low. What their audience is these days, who the hell knows.
A penny and a half per user per month.
This company turns 10 next year.