.Minato didn't needed SM against Obito , why use something you don't need + remember it always takes time to gather senjutsu , Minato didn't had the time back then .
.How are those scans not give you hints ? Minato had a contract with the toads , just like J - man & Naruto ...he having a contract pretty much tells you that he probably even went & knows Mount myoboku . I agree as a Minato fan never thought he would actually have it , but I always did wondered & now that it happened it does make sense , if you look back at everything .
.Why would he use it against Jubito? , when BM is stronger than SM + remember that they found out that senjutsu would work against Jubito in the middle of the fight & it worked by fusing SM & BM like Naruto did , which clearly shows that Minato probably couldn't do that .
.And are you telling me that Hashimara can pull SM that fast but Minato can't ? keep in mind that Edo Tensai probably came into play & made it easier to transform & if that's not enough for you ........before Minato went SM , Madara was giving a speech , which clearly gave the opening to everyone to prepare , including Minato .
Just my two cents . Minato was known as a prodigy/genius , this shouldn't be much of a surprise , why do you need to read the words "Minato also knew SM" in the manga to not call it an as pull ? ......Kishi is always giving hints .
You want as pulls , wireless Susano is more of an ass pull than what Minato did .