One thing that could be done to help AST with solo content is giving them alternative tools to spend their buff resources on for much higher personal damage. The damage isn’t stronger than buffing DPS jobs, but when alone, it makes the job less of a slog.
As a really simple example with current ASTs design, imagine if Divination were a 2-part action. You first activate Divination, then you either recast it to provide the raid buff, or you can cast an enhanced Gravity that has a very high potency, like maybe a 700 potency attack or something. This does not resolve the design concerns with AST, but that logic could be used to make it more functional when solo, including for stuff like deep dungeons and could be in addition to other changes.