Really???
I agree Kakuzu have chances but if Minato summons all the toads Kakuzu's scr**ed, I've seen Kakashi surviving/doging Kakuzu large scale elemental attacks. Gamabunta can jump freaking high and he also has water release techs as shown in fight Naruto vs Gaara, not only oil combined with fire. Ma and Pa's genjutsu doesn't count anymore??? Speed doesn't count anymore? Sealing jutsu doesn't count anymore???
Space time barrier, great defense with Minato speed defends him from large scale attacks, he doesn't need any other Kunai than the one in his hand to perform it, the location he may choose freely as shown in the manga when he was wondering where to send Kyuubi's TBB, also I'm pretty sure TBB is faster than Kakuzu's elemental attacks.
Kakuzu doesn't have enough power to hold his ground against three giant toads, Ma and Pa and Minato. Since you assume and state it's plausible for Kakuzu to shoot out all his tendrils in all directions, I will assume and say it's plausible that Minato's contract seal would deprive Kakuzu of the control over his masks/hearts. It's as much plausible, we haven't seen any of them doing any of those...
Kakuzu has chances, but if he's caught in frog's genjutsu he's as good as dead
Minato's speed comes from his Kunai....due to Kakuzu's AoE attacks, Minato's Kunai are destroyed or scattered to where they cannot be used to approach Kakuzu, but yes they provide an escape route. And yes his attacks can be dodged, but over the course of time, it is easily possible that he can be caught by them (as Kakashi was caught by Air Pressure Damage).
Summoning all of the toads take large scale chakara summons...during the Pain invasion, Ma Summoned Naruto and Pa, and Pa, who gathered up chakra, summoned only the three frogs (and even then took a large chakra consentration...and this took time as I recal).
Yes the Space Time Barrier is a great defense; however, the point is that if he has to stop to absorb the blast, he's left open from the sides for Kakuzu or his masks to attack.
Minato's contract seal was used to separate the Kyubi from Obito. As its name, the jutsu breaks a contract that has been made....Kakuzu has no contract with his masks so they cannot be sealed.
We have in fact seen Kakuzu using his tendrils in all directions. From his hands and from his back that can cover practically 360 degrees. Also his Earth Grudge Transformation showed him having Tendrils all around his body.
Finally, the Frog Song genjutsu takes precious time to build up as seen when Ma and Pa didn't immediately use it against Pain. Kakuzu isn't dumb enough to let people just sit there and build up. The Speed of the TBB to Kakuzu's elemental attacks are varied....Gidan and Air Pressure Damage appeared to be as fast or Faster....it was hard to see, but Cranium Carver appeared to be a rather slower, but still AoE jutsu.
Also, Gammabunta's Fire/Oil tech came from his Oil and Jiraiya's fire if I remember right.
The thing is that without knowledge of ftg kakuzu won't know when Minato is gonna come out from kunai. Even S rank ninja t Mintos time who knew what Minato is capabl of were told to flee on site. The reason for this is simple. Kakuzu won't be able to react fast as th speed of light. On top of this kakuzu doesn't know much about minato. Unless u can prove kakuzu has instant reflexes like killer beee.. kakuzu still gets marked by surprise.
At the same time, Kakuzu was able to survive Naruto's Rasenshuriken (though he was unable to move). Under this context, Kakuzu would likely survive a rasengan, and as such, could come up with a sneak attack while Minato's guard was down....exactly what happened to Kakashi.
Also, Kakuzu's hand seal for Domu was fast enough to where only Kakashi with his Sharingan could notice it. Now Minato's attack outside of his teleportation is virtually impossible to follow; however, between the throw of a Kunai, and its arrival by him, Kakuzu would have time to move. So I can't see him having no time in bringing up his armor.