Guild Wars 2

Hello, I’ve been discussing with some guildmates about ascended and legendary items.
I always had the idea that endgame equipments should be better than normal (exotic) items, because they are hard to get, taking lots of time and farming.
Why GW2 endgame gear is only about 5% better than the exotic?
That does disencourage people to work hard for it.
Such hard work should be rewarded with, lets say a 15% better item than the casual equipment (exotic).
Am I the only one that disagrees about lots of farming for only a 5% upgrade? Am I missing something?
I’ve been told that such a difference would break the meta gaming and lead GW2 player base to ruins, but I don’t see it this way.
What’s the problem with people working hard for some objective, expecting to be fairly rewarded, benefiting from the upgrade and being substantially more powerful than casual players?

Thanks in advance (I’m looking for constructive answers, this question is really bothering me, perhaps more than it should)