Please implement a system where sub skills are shared across all subs.
This is a simple fix which would improve quality of life so much.
Don't get too attached to this to make it fully customizable at starts, make it modular development, because honestly, stage 1 would fix most of the issue here
Stage 1 - all sub skills stay after sub change
Stage 2 - every sub can select different skills
Even if this is not in Your plans, Maximus please consider responding, I would like to know Your position on this.