I don't think that "normal give and take" implies equal at all. A good relationship is not one where its members concern themselves with exactly equal contributions, only that there is productive exchange.

One example of a particularly influential school of therapy which does advocate for therapists' self-disclosure is that of Rogerian therapy, a.k.a. person-centered therapy, which has been around since the 1950's, and which refers to it as a core element of the six "necessary and sufficient conditions required for therapeutic change":
Most contemporary critical psychoanalysts also advocate for it; maybe some of the old textbooks need to get caught up.. probably most of all though, a large majority of individual therapists just need to work harder not to fall into seemingly convenient but unproductive habits of so wholly cloaking themselves from the process.