I've been using Technitium for about 3 years and I'm with you.
Whenever I think I get it, I search for the solution to a problem I'm having and see the developer respond and feel like I get less than half the things in the explanation. My setup definitely works and it has never failed me... but there are a lot of things where I don't understand why at all and yeah I am also using maybe 10% of the options available. I'm not sure I'll ever get past the intimidating phase.
In my experience, majority of therapists are garbage. I've experienced the same, but once you get one who actually shows up and is actually good at what they do, it's worth it.