It's a teamwork, neither Sasori nor Itachi will fight alone against the respective Sannin. Using the Mangekyo, all of the Sannin will carry the constant rist of being beaten with one eye contact - avoiding any eye contact leads to a major advantage for Itachi and Sasori (especially when Itachi can use Genjutsu without eye contact, too); consequently a lot of more openings are created for the Akatsuki members. Considering Jiraiya isn't summoning all of his toads at once, the summonings can either be Amaterasu'd or controlled. A usage of Satetsu Kaihō would also lead to a big problem for the summons and would spare Itachi the waste of Mangekyo techniques on the summons.