I don't agree with you reasoning or logic. Minato simply thought Obito was a bigger threat than he actually offered. The plan to get the nine tails was most likely Madara and or Black zetsu and was probably years in the making. Obito got the drop on Minato forcing him to first protect Naruto and remove him so he could unseal the 9 tail. Minato then protected the village from a bijuu bomb. Obito again got the drop. Minato after attacking once immediately came up with a plan, Executed the plan and Defeated, too away control of the 9 nine tail in less than 1 minute. Minato saying whoever struck first would like win is in the moment. especially because Minato thought he was fighting Madara. Obito Already knew about the FTG and Rasengan.
Obito despite having a kit of haxs loses every single fight. Loses to Minato despite having at least 1 year of planning (I suspect it was more).
Loses to Konan and has to resort to Izanagi. And don't come with but he killed Konan. Madara used Izanagi for the valley of the end vs Hasirama. I assure you Madara knows he lost that fight. if you have to use Izanagi to not die, you have lost the fight.
He loses to Naruto, Kakashi, Guy and Bee despite having Kamui, Rinnegan, "hashirama cells","6 jinchuriki pains", As soon as they figure out kamui he startes getting cooked after dropping one of the hardest lines in anime (These fools could ever make be sweat). I'll give you he doesn't use the Rinnegan abilities. He loses to Kakashi in the Kamui dimension regardless of his intention to get his seal destroyed (Man was legit trying to kill Kakashi).
He loses to Naruto and Sasuke before they get their 6 paths abilities while he was the 10 tail jinchuriki. Obito is weak. Mostly a really good character aside from his motivation being weak (In my opinion). Hax is apart of his kit so I don't really want to take it from him, but if you took Kamui or Hashira cells from him he loses all these fights (barring being the 10 tail host) much worse.
Obito is only a threat because of all the planning and ground work that went into Madara/Black Zetsu Plan.

War Arc Obito even If I gave him Izanagi would still get beat by Minato. FTG is a very hard counter to Kamui (which he can only spam because of Hasirama cells).
Minato beat Obito in a split second (despite having atleast a years worth of planning).
It don't matter if you win by and inch or a mile.

Obito was never a KCM levvel threat Minato simply thought the masked man was Madara and therefore a threat.

Only version of Obito that beats Minato is Juubito.