Ultimately if you do want to switch between using a Techter and Summoner main, then you will have to just get multiple trees especially for the likes of, well both Techter and Summoner since their tress would look radically different if they are used as a subclass or a main class.
Gunblade has extremely limited use still, and if you have Techter anywhere on your class selection then you will have multiple ways to get pp regen anywhom. Have you tried using Cery/Popple?
I'm not sure where you can claim this accurate intel, but I did see the video you linked and ultimately I don't really think it's a good representation of the potential the class. The person is doing SH content as lv91, what a surprise they don't take a lot of damage but I can tell you they sure aren't dealing a lot of it in return. They don't activate Wand Lovers/WGE during their testing so the video in whole is just ???