I doubt RQ really gave other games, or at least D&D, "a run for their money", though it was definitely popular for a short time. I wasn't even alive at that time but I'd hazard a guess that RQ was probably successful due to its novelty (a focus on skills and a d100-based core system mainly) and the fact that there were so few rpgs on the market at the time compared to today's bloat. Nowadays RQ has faded into obscurity somewhat, surpassed by its little brother CoC and with the fantasy RPG market filled to the brim with far more streamlined and probably objectively better systems. Not saying that RQ isn't a solid game, but the mechanics that Chaosium is hearkening back to in RQG are quite frankly a bit outdated in my opinion, doing away with several of what I see as improvements made by Mongoose and TDM.
Apologies to the RQ elitists out there.