I may regret asking but how are players able to spend two days with a game and find broken shit that the entirety of QA and developers didn't pick up on in the course of development of the game?
Some players have a knack for this type of stuff.
Tokido is a great example. He doesn't even play Marvel that much (compared to Americans) but he played with Vergil/Strider for like a day in the pre-release phase and said that they are the best of the newcomers (with Vergil being insane).
These players can just find the cheap stuff real quick. It's hard to explain but it's not that uncommon.
Another example although not related to fighting games but to other games is Kripparian. Whether it's Diablo, Path of Exile, Warcraft, Hearthstone... no matter the game he finds the cheap/broken stuff fast because his theory craft is just that strong. Like for example... Blizzard would put out a new item for these games and Kripp would take one look at it and say "yup that's going to be broken" and he ends up being right like 90% of the time. Now you ask "well how can Kripp do that without even playing the game while Blizzard and their QA didn't pick up on it?"
According to Blizzard, most of their concern when coming up with something new is more geared towards how it plays, functions and how fun it is. Number tweaking is easy for them and comes later... they let the community figure it out and then tweak accordingly. I play tested a bunch of PTRs for Diablo 3 and gave a bunch of feedback (what's broken and what isn't) and a lot of it went through but initially when making new stuff they are more concerned with "how does it feel?" and "is it fun?" rather than "is this 10% too strong or 5% too strong?"