That’s fine, but it’s one thing to approach an existing belief with scepticism, quite another to imagine an alternative that actually triggers a paradigm shift or major new invention. When you’re basically asking, “Why can’t our rebellion come up with a technology I know about?” the answer is generally going to be, “Because however convenient it might be, people often go centuries without coming up with all the ideas that are possible at their tech level.”
You make a good point that there’s a greater incentive in the gameworld than in ours to experiment with blood transfusion. It would also be easy to say that the first few times it was tried, it made the receiving Theurge deathly ill without any notable positive effect, so it was deemed a dead end. But I’ll give it some thought.
What it certainly won’t be is a way of smuggling any meaningful quantity of already refined blood through a Ward. The concentration of aether in refined blood would keep you stuck on one side.