Compared to Evolved Diamonds, Naturals appear 'easier' to earn (and are statistically better than Evolved overall) thanks to Diamond relics and shards. Naturals kinda makes Evolved Diamonds seem like over paying for a cubic zirconia.
You only need to pull 25 gold cards to be guaranteed 1 Natural Diamond.
1-10% PF earns you 1 gold every 3 days. Without opening relics, you'll get a Natural Diamond in about 3 months, I can't even collect 3 Essences of the same type in 3 months...and by opening relics you could (luckily) get a Natural much sooner (either hitting one outright or hitting a gold).
So, fine, getting a Natural Diamond might be 'easier' than an Evolved one, but, as cappatacus and other have said: Unlocking that potential comes at a much higher cost/grind. It takes 10 keys to fully unlock a Skill Tree. If Diamond keys are only obtainable via the Rift Battles and Coins, who knows how long/difficult that's gonna be. Then there's Skill Points/CanopyCoins...which you have to manage between any fighters you want to improve, if you're always short on those resources for Golds, image how that's gonna be for Natural Diamonds...
I dunno, we can only speculate until the update hits. But, I think I'll have a Natural Diamond before Evolving one (I currently have 15 Golds: 1 for each chara and 3 with dups. 1.5 Essence of each type) OTOH; there a good chance I'll have a Maxed out Evolved Diamond before Maxed out Natural one (Maxed out means Level 60 w/ full skill tree and Max Level MA).
Regardless, new variants are coming and I don't care what Rank they are at. It's Showtime!