As others have said, your problem was oversteer that was made far worse by braking. No ESP/TC/ABS can fix this for you at that point. Braking transfers more weight toward the front of the car, making the back lighter and worsening the rear traction and causing your total loss of control and spin. The correct way to handle this situation in the future would be to gently decrease your pressure on the gas and continue your turn into the corner. If you have 4WD/AWD, and you believe, based on how the car is handling, that you still have good traction, you can also gently accelerate. This will cause the wheels with good traction to propel your car forward in the direction that you want and can correct the oversteer without spinning out. I would not do this with a RWD Benz however. The results would be unpredictable, just gently decelerate. If you abruptly decelerate, you can also transfer weight to the front and worsen the oversteer to the point of losing control. If you were truely hydroplaning, you would have likely had no control at all and propelled straight on in the direction that your car was headed when you started to hydroplane and into the guardrail, field, etc. (as opposed to spinning out)
I will never own a non 4WD/AWD car again because of what I believe is better control with AWD in certain situations. If you can have better control, you can avoid some accidents. That is a variable I can control and it is worth the extra cost to me, including limiting some engine options, etc.
Before the wife and kids era, I had a certain German AWD sports car and I used to drift (forcing the above situation) all the time. Loads of fun, but more tricky with modern AWD, the computer and system usually compensate too fast, and you need a lot of power. I actually did it the other day test driving an AWD M45 on some windy back roads by accident. It drifted pretty easy for an AWD, the tires must really suck. After I did it a couple more times the dealer asked if I knew what I was doing. I just laughed. It did catch pretty quick when I hammered the gas coming out of the turn.
Now that you understand what happened, you can be better prepared in the future. Tell your wife/GF/children about what happened and how to avoid the same problems. I don't want them hitting me some night!
One of the problems with driving in the US is that no one really learns how to drive correctly. My father took me out all the time, in all driving conditions, for a whole year before letting me drive alone. Personal experience behind the wheel is the key to avoiding accidents, and situations that cause accidents. The above is true BTW, I have a professional interest in pediatric trauma and there is ongoing research regarding what causes new drivers to have accidents and near misses. It's really interesting, and amusing. The key is personal experience, and you can't get that by driving around with dad in perfect conditions on suburban streets for a few weeks and some poor drivers ed classes at school.