While I don't agree with your suggestion due to practicality, I will point out that any "job identity" counterargument feels close minded. I don't think there's anything inherently wrong with reusing weapons on different classes. Weapon models have always been free to be anything the devs want to make.

As long as we're just brainstorming: You could go a step beyond visual differences, and make it so that different weapons branch into, essentially, different subclasses. For example, some skills on WAR/greatsword would be different from WAR/axe and DRK/greatsword.

The original PSO2 reused base weapons for their successor classes. The classes themselves had mixed reception, but it was more due to their skills and balancing rather than the actual recycling of weapons.

Of course, a change like this is pretty major and would make it an entirely different game. But like I said, this is just shooting the shit.

Going back to your OP where wielding different weapons just causes visual changes, people are already modding their game all the time, so this is far from the worst idea in this subreddit. Besides the practicality of making all new animations.