Is it the therapy technique or the relationship that heals?

You have reached the point where the methods are second nature, and now the deeper question surfaces. It is an honest one. The truth is you are asking about two things that were never really separate. The technique gives you and the client something to do together; the relationship is what makes the doing safe. You do not have to choose a winner. A person heals inside a trusting bond, and the method is often the shape that trust takes. Your skill with approaches is what lets you stay present instead of fumbling, which is itself part of the relationship. Rest a little easier with the not-knowing. One small step: next time someone gets better, ask them what helped. Their own answer will teach you more than any theory about which one mattered.