I agree, watched 1000's over the years since tube started, unfortunately a lot of crap to filter through these days, very messy.
Depending on requirement/subject matter;
No intro usually = poor content, hold, likes/subs.
15+ sec intro, some ~1min (skip) with poor res/editing and track, some that near blows your eardrums, but then can't hear content, usually = poor content, min likes/subs.
A Quick 5-10sec max where its obvious they've spent a lot of thought/time on it, not rushed, creative/different/entertaining, catchy track selection most important, used consistently for a year or more (like the tubers who get Huge sub$) seems to be the sweet spot.
I was impressed with your knowledge/selection of track grabs relevant to scene, very important for hold. Depending what area of the industry your working in, your employer/s would be crazy if their not taking advantage of it, perhaps they are.