The parent’s characterization is fine. 9/10 times (more in my own experience) it is the functional equivalent of a sponsor blocker. That it technically isn’t that specifically is immaterial, because if it works, that’s because people are skipping the sponsor segments in large enough quantities for it to easily become that.

That said, I don’t think YouTube owes it to Premium subscribers to add a sponsor block. That’s part of the video’s content as it was provided to YouTube, and YouTube never advertised YouTube Premium as something which will block in-video sponsor reads. This is part of how YouTubers make a living & a Premium sub doesn’t replace the money they receive for those the way it does for YouTube’s own ads.