In +15 you're getting 262ilvl items which are upgradeable to 272 after receiving 2500 rating.
You are also getting a totally random item from the weekly vault at ilvl 278.
While mythic raiding rewards 278ilvl straight away and 285ilvl for the last three bosses.
I think the system is fine as it is.
What's the point of that question?
Every boss of mythic sepulcher take less time than any M+15.
I know where are you coming from, but that comparison is just bad.
I don't agree with the OP, but I also don't agree with you.
I think we should worry what other people are getting in the game. That's the reason why there's an option in LFG to put the minimal ilvl.
And yes, it does diminish the work. If a random player is getting 278ilvl BIS item the first week after being carried in M+15 and some pro, who does 8x M>15 and kill 11 mythic bosses still doesn't get the item after a few weeks then it's really unfair.
The difference is still miniscule, because the pro will have much better gear in less time, but the problem still stands.
The reward should be equal to the effort.
Random BIS items drops cause faster burn out and irritation.
The system isn't perfect, but it's the best as we've had in this game for now and I like it as it is.
EDIT:
You know what? I'd actually put 278ilvl items in the weekly vault only after receiving 2,5k rating, so it would make it more fair.