So I'm solidly shifting my thoughts on Thjazi think the thing tripping me (and a lot of people) up with Thjazi is no longer "was Thjazi a good person", because as we've met him, it's become too vague. I think the better question has become "does a person doing great work on a macro scale excuse the harm they cause on an interpersonal level?"
The work Thjazi did was and is, objectively, a good thing. This ritual is a net positive that has changed the face of Araman. That is unquestionable. And therefore the pro-Thjazi side of the table are incredibly defensive whenever anyone doubts him, and they have good reason for that defensiveness.
Thjazi also stole an artifact from the Sisters of Sylandri, a religious and cultural group that he was not a part of, with no explanation or compensation, for use in a ritual that they were not consulted on. Mara excuses this with "well the stone of nightsong is serving a better purpose, now," but that doesn't change the fact that they decided of all the fey artifacts, this was the one they wanted/needed to use, and the keepers of this artifact didn't need to be consulted.
In keeping people out of the loop for their own safety or for the safety of his plan, he wound up involving Azune and Murray in a plot much larger than them that could easily ruin their lives or get them killed. While his intentions in this are logical and not malicious, the fact that he decided their level of knowledge and involvement in his plans means that they weren't able to make an informed decision about what they wanted to take part in, and couldn't offer aid that may have made these plans go better.
And, while Thjazi was trying to break the control of the sundered houses and free the afterlife, he used Bolaire as an object, seemingly thinking him as inherently less-than the people he was championing for. And this, I think, is the space where interpersonal callousness leaks into the macro scale, because in viewing Bolaire as an object, he then assumed that the other Panto masks could be similarly regarded. He took yet another artifact that didn't belong to him because he needed it for something important, and now it's attached itself to the Lady Cormoray and is going to cause immeasurable hurt.
The good things he's done cannot be questioned. He is not a secret villain, he was not duped or in line with the Sundered Houses, the work he set out to do was important and necessary.
Interpersonally, he was callous, at times cruel, and from what we can see of the flashbacks, rarely slowed to consider whether or not he could be in the wrong, or if what he was asking of his friends and family was too steep.
Both of these facts exist at the same time.
So which is more important?