Can be true, but there are boots and there are boots.....as indeed there are different wellies , both in terms of flexibility and type of rubber.I find certain wellies have far better grip than boots I've tried (seems to be a result of more flexible sole giving greater surface area on the rocks)
Each to his own. I used to wear wellies, and maybe in some parts of the country they can keep your feet dry and then it would be worth putting up with the negatives .