There are different ways to spend time. For example, you could spend the time learning how to master the game, so you can overcome a gameplay challenge and get a cool legendary item as a reward.
Or, you know, you could spend that time killing the same boss over and over and over until it drops that one item you covet.
The former measures your skill, the latter measures how hard it is to bore you into quitting. 
RNG is not the best solution, but it could be good enough. Unfortunately, what we get is neither “best” nor “good enough”, but “cheapest”.
There are ways you can use RNG to make players more empowered. I didn’t want to derail the thread, but there seems to be some interest, so I’ll try to write a short version of what I wrote a few times before.
Imagine bosses didn’t drop the legendary weapons, but instead different components required for crafting of those legendary weapons. You could still give bosses loot tables with percentages to drop this or that component, and that way you can still control the “rarity” of the legendary weapons, but now the player feels more in control.
“Oh, I have 10 ancient dragon heartstrings, 5 piles of giant king bone dust, 3 vials of black blood, and the crystal heart of the avalanche. Should I go to the Volcanic Forge to craft the Reach of the Red Mother, or to the The Forge of Ymir to craft the Bloodstone Sword”?
Obviously, I’m making shіt up here, but it’s just to illustrate the approach.
Just out of curiosity: why? I never really understood this.
Why does it matter whether weekend players have the same gear as you do? Shouldn’t skill matter more?