At the minute, if you have a really bad or broke weapon for your level like a crab whistler, it's hard to upgrade. Because of the minimum weapon requirements, you can only buy say Ataghans and upwards, but its hard to get 5k kudos to afford one training with Crab Whistlers. That was worded terribly.
TL;DR: Minimum weapon requirements shouldn't matter if the weapon you are trying to buy is better than your current one.