Broken? No. Frustrating? Absolutely. I find it incredibly frustrating to play against spammers and button mashers, mainly because I cannot play my normal game against them. When I am trying to do actual combos and difficult moves, they just keep throwing fast A's at me and interrupting. Now in a match against a normal player, this does not bother me, because that is what they should be doing. However most spammers and mashers are not actually doing combos and they just keep doing the same moves over, and over, and over the entire match. The annoyance then skyrockets when they start doing it with a character like Taki, who has the fastest A in the game (9 frames IIRC). You cannot grab them because at any given time they are pressing more or less all the buttons, guard impacting online is a gamble at best with lag spikes, and you are forced to just block and punish while trying to guess what direction to block (because even they don't know what they are throwing at you next).
I do really like SC4, don't get me wrong, but I also however think that button mashing and spamming can take you a lot further than it really should be able to in this game. Especially when played online.