Lead in Body work is the best. The good stuff. But, it takes a good man with an oxy/act torch to do the work and not warp the surounding metal with too much heat.
Most body work today is done with spot welding new panel and basically gluing (bonding) everything together. That is the new technology, but on the old stuff, gas welding, shrinking metal with heat and working metal with dollys was the usual.
Bondo or putty or that stuff never was any good if over about an eigth inch thick. Major work done with this stuff will not, does not and will never hold up.
FInd and older body shop and you'll find this ability. But, remember in this day and age, time is labor and labor is expensive. But, you get what you pay for in good body work.
There are people that want to see these trades and technices continued and may be willing to show you what to do so the art is not lost.

 

The best way is to knock out the dents as much as you can, then lead fill and file it. If you want to do it yourself, you have to have a good eye. This is how i did it. The best part, is that you can find lead lying around everywhere. Battery terminals etc. So its cheap. Then, do your panel warping and minor stuff with car bog. Never use car bog on straight metal, always use it after the primer. Your just asking for rust if you do that. But, yes, lead filling is the best way to go.