Yeah it is early to say if it's bad or not but I agree that it's a bit disheartening to put in effort and evolve gold characters to diamond, only to have natural diamonds with naturally better stats come up. With the possibility of them having better SA's, but the more the merrier I guess!
I do remember that diamonds are end game things which should only really be available to end game players. I think they might make a relic for that but in order to obtain the relic it might be through rift battle coins, then they'll be locked behind a giant wall of rift battle coins where they would have to be the strongest around in order to gain the relics. Or at least that's what I think. There are many ways to allow diamond fighters to exist but to also limit their availability to the audience.
Either that or some sort of special relic that's only available to players above a certain level. But like the above quote says, it's too early to say anything.