I still don't see the point of a strategy that has two healing classes taking turns to use the same skill when said skills overwrite one another.

A WHM stacking regens with an AST? Sure. It's going to overheal like crazy if you AoE spam it and you'll be a little squishy from a lack of shields, but it's doable.

SCH and a Diurnal AST? Easy peasy. SCH's new burst ability helps cover for AST's lower healing, and AST's buff roulette is plenty helpful.

WHM and SCH? Old School.

WHM and Noct? Just fine. AST's ST burst healing and shields are plenty strong as long as its MP holds out, so keep feeding the AST the Ewer card and you should be just okay.

SCH and Noct? No. While the shields that AST and SCH are probably roughly equal, not being able to stack them means a lot of wasted MP, and AST can't burn MP like a SCH can. Much better to go Diurnal and pop regens.