You can strongly influence the type of things on the front page of Youtube by clicking on things in your recs and selecting "not interested". The entire front page of Youtube is customized based on the type of videos you watch. Stick at doing "not interested" for a little bit and you can change the entire lot. You can make the whole thing funny animal videos or historical documentaries or whatever other niche or mix of niches you want. The main thing to realize is that repeated use of the "not interested" option is how you train the algorithm to stop serving you a specific type of video.
The only thing that doesn't seem to be included is the "Trending" tab.
EDIT: for example my front page currently entirely consists of QI shorts, retro gaming videos, horror movie reviews, and general short tech/hardware videos. The rest is stuff that's recommended based on my subscriptions, and subscriptions are entirely things I chose. If you go to the front page of Youtube and see some sorts of videos you don't like, that's not Youtube's default, it's crossed referenced things you've watched before and you've declined to tell it otherwise. Click the offending videos and mark them as unwanted.
EDIT: As an experiment I will make my entire front page of Youtube be cat videos.
EDIT2: Ok, I clicked my first cat video but youtube is now smart enough to put mostly QI videos etc in the autoplay. It used to default to stuff that's like the current playing video, but they changed the algorithm. Training Youtube to be nothing but cats will be harder.
EDIT3: ok about 15 minutes after watching a few cat videos, deleting all subscriptions and repeatedly removing all recommendations and refreshing the page, the first cat video has appeared in recommendations. They made it harder to break your account by watching cat videos, but it's do-able with effort.
EDIT4: ok unless I watch more cat videos it won't put more than one in the recommendations. Have watched a bunch. Now the main page asks me if I'd like to subscribe to topics such as "kittens" as well as tech/gaming/uk-comedy topics. This is working.