Of course player knowledge and skill matters. But there is a line, admittedly a fuzzy one. I see player tactics making a huge difference in the games I play, I've run simultaneous groups that were the same level and challenges and 1 group was significantly more effective than the other. On the other hand I think you cross a line if you are selling the DM on an idea of how your approach is so amazingly good that there is no need for a check whether or not it would actually work in real life.
I'm picking a bit on the "tank trap" idea here, but even if the PC did come up with that idea did they know how to execute it correctly? Would it really be useful against the opponent you are facing as opposed to other defenses? Why is it different than simply stating that you're setting up a defensive line with sharpened posts that will be different to cross? That, and if you PC background is that of a sheltered acolyte who has never read a book on warfare in their life, it strains credulity a bit.
So there's nothing wrong with coming up with good tactics. I just don't care for it if the benefit gained is too overwhelming or powerful.