What? No, no. Firstly, double XP hasn't "always" been done. In fact, double XP in online gaming as a whole is a fairly new concept. It's something that ruins game communities today. Another great example is call of duty, which I hope everyone can agree is vile due to it's extremely inadequate and immature target market. It strips dedication and advocates laziness.
Secondly, 50% is actually a big boost. You make it seem like it's inconsequential, which to me seems absurd because if that were true they just wouldn't add in anything at all.
And lastly, I don't care how much time it takes nowadays, there are still a HUGE amount of people in RS today with skillcapes whereas in 2006 it was nearly impossible to stumble upon someone that had one. Garrett, idk how much you played then, but I know you're a long time player so you of all people should know this. The difference between probability of finding someone with a skillcape now as opposed to then is the difference between finding a millionaire to a billionaire. It just didn't happen back then.
Bottom line, double XP is bad for business, earned or not. Games that go down that route end up with shitty communities with a game that has an unfair playing field.