Sort gems by gem level is just "1" & "2+". Sort by base level puts all skills as base level 1.

I would expect that if setting the gem tab to sort items by gem level, each level would be its own section.

Instead, it only splits in two.
A section for level 1 gems, which is naturally only support gems and uncut level 1s.
And a section that is "2-19" or whatever the highest level you have is, with all other gems cut or uncut in it.

When sorting via sort items by base level all cut gems are considered to have a base level of one. Only uncut gems are sorted into higher levels.
A lot of these skills require a minimum gem level that is higher, but are still placed with the 1s.

Yeah it seems like the gem tab is pretty well useless...