Yeah.....don't like your strategy lol.
My most successful strategy is similar in approach to yours. I offtank as a war, pld main. I actually stay off the boss almost entirely and instead do slime gathering. Due to the nature of getting the unlucky extreme far side slimes, I usually hang out on top of the furthest hexagon til slimes spawn. Then I alone grab a single slime and feed it to cadeuceus as a range dps whittles it down alongside me. With any luck the snake splits generally after the second slime, in which case I grab the second snake due to it having zero hate (provoke's incredibly handy here if healers get spam happy). At this point, no more slimes, just whittle the snakes down as hard as possible, usually with the dps split and trying to maintain even health til I normally bite the bullet and pld preps hallowed ground for the remerge. At this point lb3 from a melee dps and he usually dies seconds after, otherwise heal spam and hope for the best. We try to keep 2 melee in for triggering his rear AoE attack, which is a great breather for a sec (I used to use that suggestion on the final boss of AK too when people still sucked gear wise). Honestly, if the dps is there and the plds or pld and war are competent, and the healers don't leave slack, Cadeuceus is just a pretty easy zerg fight. Turn 2 is in my opinion WAAAAYYYYYY HARDER. Unless you're going in with 2 plds make sure your second tank has provoke, it's almost a requirement. Also, don't let other people fool you, you can't have an allegan rot rotation of less than 5 people, you should have at least 5, preferably 6 for the easiest (and most convoluted) strategy. 2 plds probably make a silence rotation easiest for high voltage, but bards work too, as does a monk if they dedicate to it. To be honest, I don't really like the left path too much because ballista on the ADS is such a pain in the ass, but that fire star patterned move is easier to deal with albeit more deadly. Whatever you do, don't let that allegan rot node fool you, totally not worth dealing with the haste boost he gets.
Just a few suggestions you've probably heard already is all.