It's not even a matter of gaining control of nodes, they can simply blackhole your access to good nodes so you end up with nodes controlled by them. Easy but loud, although it seems to be what's going on in a number of cases, and not many people are talking about it. Tor used to alert you to this, but now it's quietly tucked away into a log file. There are other vulnerabilities present in tor and the tor project devs don't seem particularly interested in them, with the DoS attacks requiring the community itself to step in with hacky solutions. I'm of the mind (never would have found myself saying this) that the tor project at large is compromised.

Monero is currently being hit by a (likely) black marble attack which is why it's so slow. They're basically flooding transactions (1/3 to 2/3 of all transactions able to be processed at any given time) so that the anonymity that makes monero work is severely degraded. Whether it breaks past transactions remains to be seen, but it absolutely weakens the anonymity of transactions done during (possibly shortly before and after) the attacks.