true, he hasn't been shown with an overpowered move. however, don't diss rasengan, it's taken down a lot of powerful shinobi and Minato's rasengan is larger than naruto's base rasengan.
True, Orochimaru, Kabuto, or anyone with a great defence has a large advantage over minato.
however.
1. chakra isn't inifinte, kabuto may be able to stay in sm indefinitely, but orochimaru definitely can't keep puking himself up forever.
2. susanoo wielders can only remain safe for a short period of time, and at a massive cost.
now, minato has the base speed to dodge pretty much anything, and then he has teleportation.
he has great raw strength (cutting hachibi's tentacle with a mere kunai is no easy feat, sasuke managed that with an a-rank tech in chidori).
he can put marks on anything, including the opponent (think a bit on how broken that is), even sparring is deadly
he can absorb attacks with space/time barriers and redirect them (possibly back onto the opponent)
not to mention, he's said to have amongst the best sealing repertoire in the manga (which he's barely had to use so far, despite fighting very powerful opponents).
that skillset makes him one of the hardest opponents to fight against. taijutsu is a no, ninjutsu has to be extremely quick or wide ranged, you need to have great reactions and a very strong defence which can be held up for a long time. only genjutsu can work, provided that you can manage to make eye contact and ASSUMING that minato isn't very good at breaking it.
so him having no powerful attack is a bit of weakness true, but a small one. it didn't hurt him one bit vs A,Bee, and Tobi