I think a blocklist is prudent for sure, and more likely for YouTube to implement. An allowlist like you propose is already similar to the pure Subscriptions vi

I think a blocklist is prudent for sure, and more likely for YouTube to implement. An allowlist like you propose is already similar to the pure Subscriptions view, and restricting it to only channels related to your subscriptions would kill most of the reason behind recommendations in the first place (virality.) Not saying that's good or right, just that YouTube is less inclined to implement such a feature.