I think you may be over-reacting somewhat.
The key issue here (which many in this thread are missing) is that young girls growing up are being given the impression that the best way in which they can be valued by society is to starve themselves silly, put on lots of makeup and a skimpy outfit, and parade around for men to lech at them? Kim Kardashian is a case in point. Its why so many young girl's main desire in life is 'to be famous'. There's so many more fulfilling things they can do; many of which wont ensure they are cast aside once they hit a certain age or start losing their looks.
I think we can do better.
You do realise that also a lot of these promotional girls also have full time jobs as well. Plus girls just like boys have lots of inspirations when growing up, when we reach adulthood we often very much never go with our dreams or we get common sense.
Also I suspect not so many young girls watch darts and F1 to be honest, young girls are far more likely to be following pop stars who quite frankly have music videos more or less bordering on soft porn, so I think F1 grid girls should be the last of your worries there. What will be next, swimwear models are banned, lingerie models how far will it go? Next thing you know wearing a bikini on a beach will be banned because of the children.
Simple fact is some one with their small minded views have decided to ban a long term tradition which actually did no one any harm and put several hundred women in jobs.
Also if you watch F1 and darts a lot of the promotional girls are far from skinny or looking starved, their is a good mix of thin, slim, athletic and even curvy promotional girls and I think times are changing where a lot of girls now realise that strong, fit and healthy or even curvy is far more attractive than looking thin or starved.
Simple facts are grid, promo, darts girls are doing no harm at all to anyone and they do the jjob because they enjoy it and get paid well.
Plus think of poor Vettel and the rest of the drivers, they now gotta stare at some guys bottom.