When I said a few 1/16ths....I meant the thickness of the poly filler shouldn't exceed no more than 1/4". Thinner is always better.
Anything above that thickness and you risk paint film cracking and/or feather edge lifting due to the fillers thermo expansion and contraction coefficient when compared to sheet metal.
If applied correctly it will last the life of the car. If the sail areas and wheel opening welds have been done correctly then there should be no flex stresses which can lead to paint film failures so bondo will work fine.
The 'Bondo' today is actually a very good product. The Bondo made by 3M is more than adequate when applied correctly.