LLMs are a black box not because they're closed or open source, but because they're based upon a neural net. yes, a closed-source LLM is more of a black box, but an open-source LLM is still a black box
beyond the error rate, the problem with using an LLM vs user-generated titles is that LLM use costs money, and we're not quite at the point of running high-quality LLMs on generic hardware yet. also, realistically titles aren't the main problem that needs solving here
also, do not underestimate petty people: sponsorblock works just fine with user-generated data
finally, the video demo clearly shows that if there isn't a user-uploaded alternative thumbnail, DeArrow picks a frame from the video to use, as is handily suggested by GP who hasn't read the article
beyond the error rate, the problem with using an LLM vs user-generated titles is that LLM use costs money, and we're not quite at the point of running high-quality LLMs on generic hardware yet. also, realistically titles aren't the main problem that needs solving here
also, do not underestimate petty people: sponsorblock works just fine with user-generated data
finally, the video demo clearly shows that if there isn't a user-uploaded alternative thumbnail, DeArrow picks a frame from the video to use, as is handily suggested by GP who hasn't read the article