It's not clear at all that 1 Twitter MAU = 1 Pinterest MAU. The really hardcore Twitter users spend all day on Twitter (@pmarca comes to mind, it seems Twitter is his full time job). I'm not sure the same is the case for Pinterest (although this might just be my ignorance of Pinterest speaking). So maybe Twitter gets more money out of each MAU because the users spend more time on the site. But maybe a Pinterest MAU is worth more - I don't know. Intuitively it feels more susceptible to "native" advertising - my little impression of Pinterest is that it consists of lots of curated glossy photos scrolling by of aspirational consumerist things. Seems very monetizable.
In any case, in order to apply your logic, the epistemic burden is on you to show that a Pinterest MAU should be financially treated the same as a Twitter MAU. I don't see that as being straightforward at all.
In any case, in order to apply your logic, the epistemic burden is on you to show that a Pinterest MAU should be financially treated the same as a Twitter MAU. I don't see that as being straightforward at all.