As a supplementary process, its fine enough. Especially in the regular medical field where followups can be as simple as "how you feeling, does it still hurt, show me a picture, etc." and not requiring the physical component of the main visit.

But let's take a patient requesting painkillers for a non-visible injury. How do doctors determine the correct course of action? They watch body language, mixed with speech, to make considerable judgements about the person from what they see and how reliable their self reporting is. Rudimentary tests are done, but all of them are often just fake outs to see if they can call your bluff.

Because that's all psyche is, self reporting. Therapists can't run tests on your mind to get anything but a few specific results, they rely entirely on what you are telling them after its been run through your mind as a filter. So getting accurate information requires not just listening to your words, but having a complete picture of your body language in all forms (just like above) to make determinations regarding what you are saying.

Somebody talking about their trauma while trembling is having a very different reaction to it than someone who is completely stiff versus someone who is quite cheerful. You might be able to hear that somewhat, but that's a gamble. And its a huge fucking gamble because that's something that your entire relationship with the client might hinge on you getting right. The voice only might be crucial to talking down in a very pivotal and bad moment, but that's a crisis reaction that is meant to tide them into the next visit.

But that's also assuming you are doing this on the phone, as the word "telehealth" implies. Most "online therapy" is just texting or a forum, which gives you the least possible info. People aren't going to just drop all barriers and be truthful as possible with you in therapy. They will try to make themselves look better, or more victimized, or many other forms if given the chance, which typing (where you can backspace and rewrite as needed) gives plenty. They will also give up very little subtle information, because how a person types reveals very little about their emotional and mental state without having a long history of knowing how they text to begin with. Its ironically less useful than just having a friend talk to you while you vent about your problems.

Which is what "online therapy" tries to portray itself as. A friend you can just unload your problems on and be magically fixed. Which does make a person feel better, but that's only if their problems were fucking low key to begin with and would have been fixed for fucking free if they just told anyone in their life.

Because Online Therapists are already very famous for being woefully unqualified and completely useless, with many many cases of them getting their licenses revoked or having clients go off the fucking rails due to them not addressing or completely missing what would otherwise be obvious redflags that required reporting. Literally everything I just typed we were taught in like Junior Year of a psyche undergrad for how important it is and how crucial a component it was to the package.

I'll stop now because you get the picture, but I could keep going on.

TLDR: You'd be better off taking the slight loss in reactivity by just talking to a fucking AI Bot and unloading your mental problems on them than paying BetterHelp (the most common and likely cheapest option) 250-400$ a month for a fucking texting friend.