Maybe modern ways have much responsiblity for the insecurities & health issues of the young esp the explosion in obesity !
Erm, how exactly? The ‘modern ways’ that I can think of all are related directly to safety, e.g safe sleeping guidelines (which surely, given that it literally saves children’s lives any grandparent would want to follow), encourage breastfeeding and discourage early weaning/food from jars. Not sure how any of those things would create insecurities or obesity 
The only other ‘modern’ thing I can think of is possibly ‘baby wearing’. But that’s only modern to the UK, has been happening forever in other countries. And has mostly stemmed from moms needing hands free to get on with things now that babies aren’t allowed to be out in prams to sleep in the garden. My nan was appalled that my health visitor would consider it neglect to do so, she asked ‘how would you cope with having six children then’. I told her I wouldn’t be having six as I’m not insane 
My own mother got very frustrated at me not doing things as they were done when she had babies. I don’t think it’s necessarily a MIL/DIL issue, more that there are grandparents who take a step back and wait to be asked advice and those who offer it without asking and, usually, are used to being ‘in charge’ and take a while to get used to the change.