Japanese Nico Nico is the 34th most visited site in Japan, so I guess they are still doing okay.
For certain things, I think Twitch is very much a real competitor, and I think the best example to answer your question, on what a competitor would need to get an in on the market - a unique twist on video hosting.
Personally I consider Netflix, HBO and Disney+ the biggest competitors. It's basically the internet version of cable vs terrestrial TV, imho. Youtube isn't so much about sharing your vacation video, as it is a platform to turn amateur content creators into professional content creators (with an odd side hustles of hosting professional music videos).