You can, but are you better than the classifier at actually doing? Have you done it for every web site you visited today?
Besides, there is some value in getting widespread blocking. When you're the only one who blocks, that's a signal. When Apple's new doodah blocks mostly-the-right-thing for 10% of the users, that's quite different. You get to be part of a crowd.
I would think so, yes, mainly because I don't have to take advertisers into consideration. And I can do a lot more for my browsing experience blocking wise, much much more.
Invalidation is hard. Once you accept you have to tread down the road of accepting and deleting cookies and local storage I see no reason to wait 30 days. Why not purge them right on (tab)closing?. If you really care about privacy that is. Which could have been set to be default on the next update btw.
Besides, there is some value in getting widespread blocking. When you're the only one who blocks, that's a signal. When Apple's new doodah blocks mostly-the-right-thing for 10% of the users, that's quite different. You get to be part of a crowd.