The thing with cross class is right now, they are all backwards compatible. Like Steady Hand II. Before if you took Culi to 37 first, you could use it at level 5 on every other class. If you took Culi to 37 and Weaver to 50, you had 6 classes with high level skills that you could 'easy button' to 50. That won't be happening anymore. After the nuke all cross class, we will be copy and paste leveling 8 classes the exact same way because even if they give all 8 classes Careful synth II at 50, you won't be getting it until 50.
As for OP, it's a grind.
Button mash to 18,
inner quiet, steady hand, Waste not, standard touch x 4, 2 Careful Synth. It will HQ enough that it will trigger the bonus experience. It's a simple enough rotation you could make a macro for it. I never have but it could be done. You do that on parts for levequests, vendor the NQ, use the HQ for Levequests and it will take out 2 or 3 levels per levequest level group. Once I have Weaver to 50 I can usually get all other classes from 20-50 in a night assuming I have the mats.