After people get past the stark fanboism they see there is not much to Rob military genuineness. Starting with Robb initial move when following his father arrest, at which point he knew nothing of the reason that led to it, he had no end game plan(unlike Tywin), he just rushed south to save dady.(after all that talk about justice)
Then he got really lucky that the baratheon brothers rebelled as well, and lucky again when his mother managed to convince the freys to give him passage i.e. the victory(without the freys he would have been lost, trying to force passage over the crossing). The frey who already given their liege lord the finger, who then lost at riverrun. The freys who didnt participated in the previous war, only joining the wining side in the end, they joinied some boy who has never fought a battle and is outnumbered, has no plan and outnumbered by half of the realm.... *suspension of disbelief*
Then he used his advantage and "won" 2 victories, in both his forces outnumbered the the lannister forces by few times. Then he returned his only card against the ironborn and decided that waiting for an asnwer from the iron born its fulish, it's obvious that they would agree to HIS plan(some boy who won 2 battles) and rush into the wasterlands(where the was owned few years ago). Again he had no idea how to get there, but luckily his wolf found him a super duper secret passage into the mountains, that no one knew about, allowing him to bypass the lannister forces and fall on some greenboys at night winning his third victory. Then he manged to ransake some countryside holdings and marry with the first girl he sleept with, breaking his promise to the freys who gave him his victory... yes.. briliant.
His forces outnumbered the Lannisters? Where? In the Whispering Wood yes. The he fought a host3times his owns size at Riverrun. So wheres the mixup there? He had some riverlanders with him but not the10000or so difference. Oxcross he was also ounumbered. He exploited any advantage he wsa given-not brilliant commanding but very good. He was helped out by George a few times-the goat trail and such. He was also habdicapped by him-Karstark and Theon betrayal. He made a mistake sending Theon but its widely regarded as a stupid move from Balon to attack the North so could Robb have forseen it?
Robbs not a brilliant commander, but his team uip with the BF is the best wev seen form a purely military view. Who can you compare to? In this the OP is correct. Stannis seems like a decent commander, as does Tarly and as did Tywin. But neither has seen as much screentime as Robb. If Stannis beats Roose hes right back up there in my opinion. Im hoping to see Tarly back up all the claims aswel