No grainfiller has ever worked for me like that. And if there is ever ANY pores left that i fill with finish, it always sinks back into the grain within a week. That is the whole reason i went with epoxy. Literally NOTHING stops finish from sinking into finish here for some reason.
The key is to seal the wood with a sanding sealer first, and let things rest between steps... but you're right, there's always a bit finish sinking in. Personally, I like that.
That is the exact reason i dont use sanding sealer anymore, since it shrinks more than anything. If it was that easy, then i could just build up enough sanding sealer until it is level and grainfilled.
I literally cant sell guitars becuase they have some shrink back into the grain. I think it looks incredibly crappy and badly done. If a finish is going to to be a smooth gloss finish, it needs to be like glass or else it isnt even worth it.