The instigation of Needle Jizo entails that Jiraiya has to perform a hand seal and then initiate the jutsu which is by far slower than Tobirama simply warping behind him and lopping his head off. The same applies to Jiraiya intercepting his kunai when his reaction speed alone was significantly faster than KCM Minato's. Strangely, your argument can be used to justify why Minato loses to SM Jiraiya which is contradictory to Jiraiya's admission of inferiority. I'm sure you don't properly grasp the tremendous speed of an FTG user.
Tobirama's Suiton also sliced off the Shinju Roots and we're given the implication that Boss Summons are susceptible to penetrative attacks given that an Anbu's Futon managed to pierce through Cerberus's leg.
You'll need to prove Jiraiya can't form a single hand seal before Tobirama crosses 50m of distance. That's half a football fields length. Don't forget, his seal speed is fast enough to use summoning jutsu to intercept Kisames slash on Naruto from point blank range so the fact that you're entertaining the idea that he'll get "bam flashed OHKO" from 50m without so much as pulling off a single seal is ridiculous, pal.
Read what I said. I never said Jman wins by using that method. I never said he wins period. I don't know who wins because I haven't thoroughly examined both parties full capabilities. I said it's not clear who wins when boss summons come out and that Tobirama isn't simply blitzing Jman off the bat with zero reaction and will OHKO him, which is what YOU said.
Gamabunta isn't really durable. Tobirama's Suiton cut the God Tree, it'd slice Gamabunta, or any other toad summons like butter.
And fodder shinobi also cut parts of the god tree branches with kunai so yeah, no evidence it's cut through boss toads because no fodders are cutting through the boss toads, especially considering they survived CST from Deva Path so Tobirama putting them down is not going to be easy ESPECIALLY if Ma and Pa come out.
