@Ruebattery It actually becomes available immediately after you invest the first three Skill Points into Dexterity Up 1.
Anyway, with 5 Skill Points fully invested in that Skill, using your SB's Weapon Action and a directional input will give you 0.35 seconds of i-frames, which is more that you can get from a normal dodge with 10 SP into Advanced Dodge.
That basically gives you the greatest mechanic-based advantage to survive with SBs; from there, it just becomes a matter of learning enemy tells and deciding when it is best to Dodge or Photon Blade Escape with the right timing. This part just requires patience and practice.
For the sake of knowing, can you recreate your Skill Tree in the Skill Sim (make sure to set the language option to "English (PSO2NA)" and post it here?