> Mastodon: ~50,000 DAU (1.4M MAU)

Hold on, are you... getting DAU by dividing MAU by 28? That's very much not how that works; perhaps the easiest way to illustrate this is by considering Facebook, which has ~2bn DAU, but obviously does not have 48bn people using it every month.

In general for social media stuff, DAU and MAU are pretty close to each other; Facebook is 2bn vs 3bn or thereabouts, and AIUI Twitter is even closer.