it's not - you have 11 0.5% chances are about 94.64% of not getting a rainbow

Effectively in ever 20 pulls is a rainbow

One in what 420 is a double rainbow.

Where as there's about a 47.75% chance of a non gold+ pull, so 52.25% of a single gold+

12.7% of a double gold or rainbow
After that doing quick calcs becomes tricky and even at this point there's some chance I'm fudging it

The pulls we are seeing makes me think the odds have changed as lots of 3/4+ and rainbows being pulled right now