I just checked some Megascans stuff, and there is no wind direction. I agree with you, by default, you only get to tweak the influence, and it does look weird.
Thing is, the main parameters are in a parameter collection. To get to that collection, go to the main material, double click the Simple_wind_material_functon, then double click on WindIntesity ( for instance ).
I found that setting ‘influence’ ( your original param ) on .5 and WindSpeed on 2 looks more real ( for the short grass ).