If you mash, you lose VERY fast. The joint lock submissions are a stamina management game with button presses. You will instantly notice Arm and Leg submissions are tuned very differently so different tactics work and even though they are both button mechanics they feel totally different.
When you don't push the button your stamina comes back, but your opponents presses are moving him towards victory. When you DO hit the button depending on where your stamina currently is, you move the submission more in your direction and deplete some of your stamina. (as the battle continues over time these button presses become worth more for both fighters). So the entire meta-game (which takes serious time to master) is about managing your stamina and has NOTHING to do with being able to mash fast (turbo controllers will instantly make you lose), and deciding when to burst through and try to escape based on how much each button press is worth. Losing all your stamina results in a short penalty where your presses are worthless (if you are being submitted) or failure (if you are submitting).
There are several different ways to play and even our most advanced members of the dev team still haven't decided what the best method is.. but the way I play it is hang on and conserve my stamina and watch my opponents stamina and mine, when he gets tired, I'll try to quickly escape or finish (the gamble here is trying to make sure I can survive long enough for him to get tired, then get swing the battle all the way back and not completely deplete my stamina doing it).
Your opponents MAX stamina (which is depleted during the fight by having his grappling attempts and escapes countered or denied) can also affect the outcome because it maxes out what his potential button press is worth, so in the end the real way to submit someone is to wear them out with some ground and pound, and go for the submission when they are exhausted, you have a much easier time in the battle... There is a lot of strategy to it. Ground fighters get quite good at setting it up and then very good at the submission battles themselves...