There are movies and shows like Dead Leaves, Magnetic Rose or Jin Roh in which the directors influence is felt in every cut and cut, in those cases, although I agree that tagging the director / AD on every post can get out of hand, I think tagging them in the source could be a good alternative.
If the AD is not mentioned, one could think that the animator credited on post is the one with most of the influence on the final product, which is in a lot of cases simply not true.

It's a complicated topic, and even more insidious than you might be thinking. You're looking at it from the angle of renowned auteurs, but people in the trenches will sometimes complain that the person they see tagged delivered super rough work that was entirely salvaged by others. Sakugabooru started at a time when layouts had a very different nuance and 2nd KA mostly still meant cleaning up shots, rather than maybe fleshing out stick figures. Keeping track of all this has also gotten a lot more annoying due to the fragmentation of the animation process.

That said, for now the way to go is mostly still the source field or comments, which are there for a reason - if people still get the wrong impression even with those there, that's frankly on them. If you know for a fact that a singular AD had a strong hand on a scene, adding it to the source field without breaking the usual formatting is fair. If they (or a kantoku/enshutsu with these proclivities) have fundamentally changed the scene, with corrections that go beyond simply correcting the designs or one pose, then that's when you actually tag them. And if an Imaishi movie looks Imaishi as hell, you can just leave a comment to say Hey, this looks Imaishi as hell, lol.