I don't see a commonality.
Here are some nice examples of bathos; there's nothing desultory about them.
Do these words ''bathos'' and ''desultory'' have anything in common? For example, in a desultory converstaion there (perhaps) might be a change from a serious subject to something less important or even silly, but what about feelings?
To think I lived almost 50 years without ever hearing of bathos before!
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.