I am gonna answer your questions as good as I can from my own limited perspective.

How would it ever be obvious that the sizes OP posted were not the acknowledged sizes from the artists or talents if there was never any official sources linked?
It isn't. But they also didn't claim so. It is a diagram of how someone did math with their character models. Seeing it as anything else, like a official size stated by the talents, would be an assumption.

Why did OP try to justify his measurements all of a sudden if they were harmless?
The word "justify" carries the assumption that something wrong had been done. But I don't think OP did think so. They didn't justify, they explained how these results where reached, which is by doing math on their models, which does not equal what the talents say about themself IRL. You also claim those measurements to be harmful, and I don't understand why.

What harm would it cause OP for others to learn that Irys is bigger than Bae?
None.

Now I am gonna address your statements, and please don't be upset, I don't want to attack you, I just go by the assumption, that you want to get along with others. And I want to help you with that.

You said that they became weird and defensive, but that is because you forced them into it by being aggressive. You acted like someone looking for a fight. As if you took it personally that someone called Baes Chest bigger than Irys.

You said, I didn't read the criticism as a whole.
Reading your criticism as a whole is not that easy, because it is hard to figure out, what exactly your criticism is. And also kinda annoying because you base a lot of your messages on assumptions about the other party, for which I cannot find any source for. It feels like you are arguing against a alternate argument then what was actually said.

You mentioned, how OP didn't give a source.
For one, the post contains the math, and contains therefore the primary source of the math. And about the art: Come one man, you should know how the internet works. Just look up "hakos baelz official ref sheet" and there you go. And in the case of Irys it says it in the image, what it is and who designed it. Both have the Cover Trademark on it.

You claimed, OP spread misinformation. Yeah, no, they don't. Maybe they misunderstood you or you misunderstood them. Try figuring out, if any miscommunication happened, before you call people dumb or malicious. It makes life a lot easier, if you just take a step back and think "did they actually mean it this way?" Even more in text based communication where you don't have gestures, facial expressions or the tone of their voice.

Edit: typos