I think while construct doesn't have perfect stability, arsonide's description was a bit of an exaggeration. I haven't used mmf to compare, but as far as gamemaker there's no comparison, it's so much faster in terms of both developing an idea into a working model, and also in terms of graphical and computational performance it's not even in the same class. I paid for gamemaker, and I wouldn't even consider looking back. Also, there are many on the boards who migrated from mmf and haven't gone back. So, yeah, stability isn't perfect, but flying to moon with bottle rockets strapped to your back is an unfair analogy. the crappy car is a better analogy, though we should say it's a beaten up ferrari.
Keep in mind Arsonide is a developer of a procedural space game with infinite (for all practical purposes) universe, that had moved away to try out Unity, and come back to Construct with continual updates on the development to his game for the last several months. Seems a large investment of time for something if he was so sure it wasn't going to work in the end. I don't think he was trying to deceive you, just warn you that stability is an issue at times. It's just the analogies he used seem to indicate it's impossible to work with construct without it all ending in disaster, which I personally disagree with.