I feel the reason Bullock's character was seemingly weak was to portray the dichotomy between her and Clooney's character. He being a veteran astronaut on his last trip and her being a fledgling first-timer in an ultra-rare and exceptionally stressful situation(s). Clooney was the light in the darkness, and when he was gone she had to go it alone, eventually overcoming her own weakness and fulfilling a pretty obvious archetype.
I wouldn't call her dumb, she freakin' got a Chinese escape pod up and running, lol. And training can prepare you but it doesn't mean you will behave the same in such a real scenario. I believe many army veterans can tell you the same.
The movie would have been very dull if both astronauts behaved like level-headed veterans going through the throes of space disaster. If anything the acting direction was supposed to play off the viewer's own emotions of utter helplessness. For some people maybe they don't get that feeling, and, like you, did not enjoy the way it headed.