MDF doesn't show grain. Many glues will clog sandpaper if you try to sand them. D fir is possibly the worst of all woods to show grain. Quarter sawn will probably show grain less but it would be a terrible waste to paint it. Sanding sealer might help but I'm thinking you might need quite a few coats of paint with sanding in between to get what you want.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.