This is fair guess on intuition but working in recommender space on both content/ad recommendation, content understanding signals have pretty consistently across two companies and many projects tended to underwhelm and key signals are generally engagement signals (including event sequences) and many embeddings (user embedding, creator embedding, ad embedding, etc).

The main place I’ve seen content understanding help is coldstart specially for new items by new creators.

And you wonder sometimes if the products being advertised, themselves, couldn't matter more than the targets reading them. We've learned to recognize crappy offering and AI can try to make me read more and more ads relevant to what I'm saying, if it's a crap product, I won't pay anyway :(