As for "fresh learners", I can provide my own son, who watched the series before taking his first linear algebra class, and says that it helped him a lot.
With all due respect yours is a very short sighted take that only thinks in passing tests. That's not the purpose of education.
In fact, your claim is strong and quite easy to test. If watching the series gives people a better fundamental understanding which makes subsequent learning more efficient, take matched novices, randomise them to watch the series or not, then teach both groups some later lin alg materials and measure learning gains on novel problems.
That's the kind of test I mean, not 'can you grind through the course exam'.
If your claimed deeper understanding neither improves what someone can do afterwards nor how efficiently they learn related material, I'm not sure what observable content the claim has.
Uh huh, and what if the videos make me more generally interested in the topic? How would you measure that on a test?
Your view seems needlessly pessimistic and myopic. Just because something might not increase a number on a test that doesn't make it pointless.