atanakar
Hero
I randomly came upon a source for my own supposition. I was listening to an interview with Lawrence Whitaker (co-designer of Mythras and other BRP games for many years), and he said RuneQuest came about when Steve Perrin decided to adapt the Thief skill system into a full percentile skill system.
Here it is, if anyone is curious: Lawrence Whitaker interview (YouTube link, queued to the time he mentions it).
Thanks for sharing. The influence seemed obvious in my mind.