Except the math doesn’t quite work like that.
Assume, for the sake of argument, that there is a 0.1% chance to draw a Mythic from a Gem chest. You then have a 1% chance to draw one from a VIP chest. Your chances of not drawing a Mythic on each pull is 99.9% and 99%, respectively.
In your example, you are investing 2,250 gems, which gives you 250 Gem pulls or 50 VIP pulls, respectively. Your chance to get one or more Mythics from Gem chests is:
Pg = 1 - (0.999^250) ~= 0.221 = 22.1%
Your chance to get one or more Mythics from VIP chests is:
Pv = 1 - (0.99^50) ~= 0.395 = 39.5%
So it’s a little worse that twice as good. If we change the probability of a single Gem draw to 0.2%, we instead get Pg = 39.4% and Pv = 63.6%, which is markedly less than twice as good.
VIP is still the best odds you can get, but it’s not a linear improvement.