AST should have one default and one toggled sect

[Seraphor]

Seriously. The very simple fact is one sect doesn't play well with SCH's and one does. And the one that plays well with SCH can play with either AST or WHM as well. So the one that can play well with any combination should be the Default Sect.

How is this even controversial?

One potential issue, to play devils advocate as it's technically a slippery slope fallacy, is that by making Diurnal the default sect, Nocturnal sect becomes irrelevant to the point that it gets removed.
They could conclude that Diurnal already has a shield via Celestial Intersection and Neutral Sect, and that Nocturnal Sect is no longer necessary. Stripping yet more identity away from AST.