I don't think anyone thinks Twitter is doing well in its own right. It's shedding users, it's possibly harming democracy, their moderation is being questioned daily in the national US press and many users don't know how to use Twitter.
I encourage you to have a look at Guillaume Chaslot's https://algotransparency.org - it identifies what videos YouTube's algorithm most often recommends, based on a given search. Serious question (I'm not trying to be facetious): looking at those recommendations, what do you think?
That is not proof. It's cherry picked topics for uncontrolled Youtube recommendations to a bot account they created. I think nothing about that is scientific and it screams tech illiteracy.
Google ads were also used substantially during 2016 [0]. Google’s ability to target messages to demographics that they only know because of their data trawling is effective for selling garage door repair and election influencing.
This "harming democracy" and "being questioned daily in the national US press", is all about the existing arbiters of information (also called the mainstream media) trying to protect their control over information dissemination.
It didn't become the next Google or the rightful FB competitor (like analysts predicted) but it's doing well in its own right.
Evernote is spinning around the drain and early employees and VCs alike are trying hard to dump their shares on the secondary market.