Actually back in sc1 win ratios for pros were lower than that. If anything it should follow an ELO formula.

As for noob starts logically they will work against people that do not know how to counter them. This is why intel is so important in sc and sc2. Normally you should scout and know he is going banshee and then defend accordingly. Even if you lose obs you can just hold with cannons as they will detect cloak. Then just build up b/c that build prevents them from building up as they waste a ton of resources on it. Effective counters like going storm would work well against big clumps like that even if you do not have detection.

Basically if you see them going mass banchee your best bet is blink stalker with obs and you just won the game.