If only that was an analogy to prove that Naruto wins. That was an analogy to show how strong Naruto would get. Your analogy doesn't even work. KCSM Naruto isn't SM Naruto plus KCM Naruto, so you can't apply the gap in power between Base Minato and SM Naruto to the gap in power between KCSM and KCM Naruto. Example:
Minato is a 4, and Naruto is a 2.
4 2
Apply the KCM boost. We'll say it's 4.
x4 x4
16 8
Naruto gets a Sage Mode boost. We'll say it's 2.
16 16
Not saying that these are the definite power levels, just showing that saying Minato>SM Naruto as evidence that KCM Minato>KCSM Naruto doesn't work. SM is a multiplier.
Since we don't know definite power levels, I'll use the variable N to denote Naruto's speed in base to prove to you that no matter the multiplier, as long as base Minato is superior to SM Naruto and that the KCM boost is the same multiplier for the both of them, Minato in KCM will prove to be superior to KCSM Naruto when it comes to speed.
Let N denote base Naruto's speed. Let S denote SM's multiplier and let K denote KCM's multiplier. Therefore, KCSM Naruto's speed is KSN. Let M denote base Minato's speed which is superior to SM Naruto's. Therefore KCM Minato's speed is going to be KM. We know that M>SN, therefore, KM>KSN thus proving my point mathematically.
Now I'll prove that after the boosts, the gap between KCM Minato and KCSM Naruto will be even greater than the gap between base Minato and SM Naruto.
The gap between KCM Minato and KCSM Naruto = KCM Minato's speed - KCSM Naruto's speed =KM - KSN = K(M - SN)
The gap between base Minato and SM Naruto = base Minato's speed - SM Naruto's speed = M - SN
Therefore, the gap between KCM Minato and KCSM Naruto is greater than the gap between base Minato and SM Naruto by a factor of K.
If FRS is used as a melee weapon instead of just thrown, then the space time barrier strategy isn't going to work. Naruto can avoid it by attacking from any other direction. Minato might have superior speed. Sage Mode amps KCM Naruto's speed by the same factor it does to Base Naruto to SM Naruto's speed and reactions. If Naruto is behind, he'll still be able to keep up and might even have the edge due to Sage Sensing (Acts as precog) and Frog Kata.
I'm pretty sure Minato can easily avoid the FRS used as a melee weapon considering it took three tries for Naruto to tag the 3rd Raikage. Just because Naruto has sage sensing doesn't mean he'll have the edge because he had sage sensing against Madara but did not have the edge. On the other hand, base Minato is even faster and the gap between KCM Minato and KCSM Naruto is even higher than the gap between base Minato and SM Naruto which is even larger than the gap between base Madara and SM Naruto. Frog kata is something Minato can't predict but KCM cloak has great durability and Kurama chakra has shown great healing abilities so no physical blows will hinder him. Also once Naruto or his clones get tagged, that target is a goner considering how even Juubito had trouble reacting to FTG once he was tagged.
Furthermore, I believe that a KCM user can have more shadow clones at a given period of time in comparison to a KCSM user. This is because the KCSM user has to balance natural energy so they won't be able to spam as many clones much like how SM Naruto can't have as many clones out as base Naruto can.