Seeing how few weapon variations there is for the new jobs, I don’t see that being anywhere near as big of problem as you think. Make 4-6 variations for low level content and commit all real creativity for the expansion the change happens in. If they want to do more they can do it gradually.
If it was as simple as “make a second gun job”, why hasn’t it happened already? SE is aware the community would happily welcome a gun job…it’s why they gave MCH a gun to being with and especially after they put on a real display of what we really wanted. I believe the reason we haven’t is because they don’t want to trivialize MCH by adding a job that mains the same weapon. The easiest complicated solution is change the weapon on the job that doesn’t need it to exist.