First of all, it just flips which side you need, and there's no reason why Tunsil couldn't flip to the right side if we draft a left. Second of all, there is no guarantee we get Tua. Tua could choose not to declare, he could have a bad year and his stock drop even within your own scouting department, someone could tank worse than us, he could get injured, etc. Structuring your team around a draft pick you don't even have yet is colossal stupidity, especially when doing so involves jettisoning a franchise caliber player at the second most valuable position on the field.