Carbon is the next version of Argon. But Hydrogen is supposed to coexist with Carbon. Also no idea where the scheme is coming from, what elements should we expect.
Wild guess: maybe they are going with how abundant the elements are to scale the models. I'm no chemist so I don't know reliably how the relative abundance of Argon and Carbon works out, but Hydrogen is "well-known" as the most abundant element in the universe, so maybe that's why its the base model. But, this is essentially a trend of one, so not a trend at all, unless someone can verify it still works for Argon and Carbon.
Intuitively, Argon is 4 Pro, Carbon is 4.1 Pro, and Hydrogen is 4.1 Flash (slightly better than Argon according to benchmarks).
The sol/terra/astra, haiku/sonnet/opus clicked without needing to be explained
A fable is a tame mythos.
The problem with using elements names simultaneously as both version numbers and product tiers, is that inevitably you will face a confusing collision or you will exhaust the space.