The issue with paying for youtube premium is that you are still left with tons of ads. Until YouTube themselves doesn't tackle this issue as it should I refuse to pay to see sligtly less ads.
I pay for YouTube premium and have never seen an ad. Not sure what's happening with you.
Half of the content on YouTube could be considered to be an ad by itself.
Also sponsors are being advertised regularly within videos which I would consider to be ads too
It strongly depends on the kind of content you watch. I watch a lot of YouTube, but hardly any of it has sponsored content.
A lot of the videos I see have ads in them, section whith "this video is sponsored by this and that". That's definitely an ad. I would say most new (past few years) content by established channels has these. Some more obnoxious than others.