But it kind of is a big deal. You can't just hit a button and your excess LD becomes a RD or RW.
In reality, those top line players are rarely available. Drysdale for Gauthier trades rarely happen and even in that case it took him forcing PHI to trade him.
For example, let's say you have a 1LD, and the team needs a 1RD. You draft the another 1LD with the intention of trading one of the excess LD for 1RD. What if that player isn't available? Now you are trading the LD for a 2RD + a pick to make up the value. That's cool, but the team didn't need a 2RD, they needed a 1RD. You could've just drafted the 1RD.
Obviously if the talent difference is huge, you don't take a guy based on need. But if it's a toss up who is going to be better, take the guy you need. If you're building a team through the draft, at some point you have to consider team needs.