I have a little "share" button on my iPhone that invokes Youtube-DL via Pythonista, so I can open any Youtube video and get a locally saved copy pretty much instantly. I can use VLC to stream YouTube videos without ads.

There's a bunch of apps that let you load pretty much arbitrary code onto the platform - Pythonista and Scriptable are two of the top ones (Python and JS interpreters respectively), and with those you can do quite a lot.

It's not the same experience - that I'll grant you - but if you're moderately a power user iOS gives you enough to work with.