9/10 dents can be taken out by a skilled panel beater. 9/10 bodyshops arent skilled in doing this though sadly. Hence the filler being used instead.
It's not so much about lack of skill, It just depends on the type of bodyshop.
The Vauxhall main dealer bodyshop that i worked at for 8 years used filler but only to finish. We simply were not allowed to spend the time required to repair without it. the problem is, we all had to work to a very fast paced schedule and the time involved in bare metal repairs would have put us behind and we wouldn't make the bonus.
Sounds bad i know but by no means was anything bodged, Dents were planished out to a good standard and any slight high spots or imperfections were filed 'true' with a body file. Then a light skim of filler or 2k stopper would be used to accurately restore the shape of the panel or swage lines to 100%. It is the only way to get a perfect repair in the time allowed.
Mind you, the cars we worked on all day every day were either new or nearly new so anything more than a slight dent or scrape would often result in panel replacement anyway.
If it was an older car (8-10 years old) then in order to make the repairs economical in order for the insurance to pay rather than write off, time allowances would be cut down and repairs would be quoted instead of panel replacement. In those cases then filler would defiantly be used.
At the end of the day who in their right mind would work on a repair for longer than they are being paid to do so? as long as the finished result is good and it doesn't have huge thick chunks of filler in it, everybody is happy!
As for private body shops, then it is between them and their customer to agree how much the job is going to cost and if they quoted for bare metal 'proper repairs' then the bill would be alot higher due to time involved and most would opt for a lower bill and a light skim of filler.
It all depends on what is reasonably worth doing i suppose.
Ben