What you say is true for old cars and old roads. The succesfull combination of modern steering systems and modern tarmac roads make it perfectly safe to put the thumbs through the wheel. If you do go off-road, than put the thumbs on the face of the wheel, but on the road - inside the wheel. They play a crucial part in the grip of the wheel.
9 and 3 does increase the leverage (amplitude). In 9 and 3 you can turn the wheel about 260 degrees in each direction in the event of a sudden evasive manuever. In 10 to-2 or 8 to-4 you get about 180 degrees. These positions also reduce the stability of your grip and your ability to turn quickly or with less effort.
Conclusion: Hold the wheel at 9 and 3.
The steering technique is more of a matter of personal style, and there is nothing wrong with the well-established pull-push technique. However, there are more effective techniques. I will not describe them because they are a bit more advanced and complex, but I can give you a few points to punder on:
1. In pull-push, you don't use your muscles all that effectivelly. Pulling the wheel is much better than pushing. It is easier and more smooth and controled, due to the use of finer muscles in the forearm and palm, rather than the shoulders.
2. In pull-push, you don't maximize the amplitdue: You turn the wheel in movements that are at best 180 degrees each. The more steering you turn for a single hand motion - the better. In the advanced steering techniques you can turn the wheel as much as 360 degrees in a single hand motion
3. In pull-push, your control of the wheel isn't as good as it can be, since both hands move up and down, even though only one hand is steering. Most of the advanced steering techniques follow a predictive notion, which means that your hands will remain for as long as possible in the basic grip (9 and 3).
4. In pull-push, you cannot steer as quickly. In the advanced techniques you can steer from lock to-lock within a second or two, and control the wheel in all and any situations, including sudden skids.