Is it correct to assume taht since general's cry support makes the supported skill attacks count as exerted and that the line in intimidating cry, ''exerted attacks deal dobule damage'' that for the duration of your intimidated cry, all the attacks of the skill supported by general's cry deal double damage?
No. Intimidating Cry only exerts attacks you perform. It has not effect on Mirage Warriors, because they didn't use Intimidating Cry.
Exerting is unrelated to buffs and does not have a duration.