True, Jiriya with ma and pa summons has a very good chance of beating kisame/itachi. Ma and Pa break him out of genjustu, he may not even need to look itachi in the eyes because of sage mode sensing. Kisame cannot aborb to much chakra or else, he turns to stone.-Susanoo doesnot block sound( kabuto's justu got through susanoo), so itachi can be taken out that way- Jiriaya can seal amaterasu. With kisame, Jiriya with Ma and Pa overpower his long range suiton, and in close combat kisame doesnot stand a chance
because of sage mode. The underlying factor to the victor is determined by wethor or not Jiriaya can enter sage mode fast enough. considering he avoided pain ( in his own village) I would assume he could avoid/stall Itachi and Kisame for long enough-although it really depends on where they are fighting. I say Jiriya hides inside the mouth of a frog the size of mouse ( way he snuck into amegakure) muntil he gathers enough chakra to summon the toad elders.
-Jiriaya is so scary because of his versatile abilties and intelignce-summoning toad stomach takes out 99% of narutoverse-His swamp justu in a weakend state got Manda, a boss summon. I have seen calcs that place his Doton justu in Sage Mode at town level range. Most people undermine him because he is goofy, but he really is (similar to naruto without PIS) a genius combatist.