Therapy is not a process where you only pour yourself out to a person and empty yourself. Even if you don't use any drugs, the therapist guides you through your emotions, mostly in a pretty neutral manner, but not without nuance.

The therapist nudges you in the right direction to face yourself, but in a safe manner, by staggering the process or slowing you down and changing your path.

A sycophant auto-complete has none of these qualities bar a slapped on "guardrails" to abruptly kick you to another subject like a pinball bumper. It can't think, sense danger or provide real feedback and support.

If you need a hole which you can empty yourself, but healthy or self-aware outside, you can provide your personal information and training data to an AI company. Otherwise the whole thing is very dangerous for a deluded and unstable mind.

On the other hand, solo writing needs you to think, filter and write. You need to be aware about yourself, or pause and think deeper to root things out. Yes, it's not smooth all the time, and the things you write are not easy to pour out, but at least you are with yourself, and you can see what's coming out and where you are. Moreover, using pen and paper creates a deeper state of mind when compared to typing on a keyboard, so it's even deeper on that regard.