It wouldn't be hard for google to poison competitor training just by throttling bandwidth.
This isn't certain. Google do not break out Youtube revenues nor costs. Hosting this amount of videos, globally, redundantly, the vast majority of which are basically never watched, cannot be cheap.
It's entirely plausible that Google's wider benefit from Youtube (such as training video generation algorithms and better behaviour tracking for better targeted ads across the internet) are enough to compensate for Youtube in particular losing money.
Google does break out Youtube revenue.
Latest 10-K: https://abc.xyz/assets/77/51/9841ad5c4fbe85b4440c47a4df8d/go...
See page 10, for youtube Ads revenue.
I mean, you could limit yourself to the most popular or most interesting 100 million, but that's still an enormous amount of data to download.
google will have access to all of these. competitors will have to do tons of network interactions with google to pull in only the first set. (which google could detect and block depending on how these competitors go about it)