Basically.

But Thomas of Aquinas thought that opportunity cost was something bankers thought up to justify charging interest, rather than a real thing.

You can't effectively price the cost of something that never happened. You can only estimate it. In fact, you don't know if it ever would have happened.

It can be an illusion if choice.
"If I had done this, that, and the other, then I would now have X," is a presumption. You actually have no idea.