Maybe that's a bit harsh... I can understand the OPs disappointment. Maybe the "almost surely lost me as a customer" was a bit of an exaggeration (or maybe not.)
QR does advertise the ability to UG using Avios on their website. Of course it's NEVER guaranteed. They also publish a calculator telling you how much the UG is going to cost. So when you are in that situation and you're quoted a price that is 50% higher, because it's within 3 hours of departure, I can understand being disappointed with the experience.