Conventional corporate hierarchies make sure that there are only a handful of managers for every hundred employees. So your chances of becoming a manager are very small. This is the same reason why only a small percentage of employees in any organization get promotions.
This means that the odds of you failing to get a promotion in the job and the odds of your startup failing to get traction are almost the same. Besides, a startup is more exciting to work on and in the long run it promises more rewards for the same amount of effort put in.
I wonder why you selected the less exciting path then.