Not a bad argument i must say

its true Orochimaru does have his chances but its never 100%
its true orochimaru might be able to blow back the kunai that minato places but he cant blow back the seals minato places himself.. once minato realises he cant place as many kunai he will resort to doing this..
another thhing is if minato manages to place that seal on orochimaru the question is wether or not orochimaru will realise.. there are moments when minato uses such subtle hand movements and quick instances where he places that seal
if a seal does get placed and orochimaru misses it then it could be fatal.. and with seals placed around the area any big attacks from oro and be redirected litterally dropping the attack right on top of oro himself
Minato can also use his kunai to redirect attacks since they both have the seals on them so oro would have to be very careful
of course the chances of Orochimaru not noticing knowing minato's reputation and skills will most likely take caution but a battle is never 100%
Also the speed in which minato can land a hit on orochimaru with his size rasengan can damage orochimaru's organs fatally even if he can heal the external injuries the organs are a different matter
we must also not forget Minato's sealing capabilities which could also turn a tide in the fight of course i cant elabourate much on these since we havent seen enough however minato can always end thigns in a stale mate by sealing orochimaru with the RDS