The proliferation of town skins and the change to the numbers that can be sent on  attacks has changed the balance between offence and defence.

Lots still sit unshielded but there is now a risk - and the bigger the complacent trainer's meatwall the bigger the losses.  At need an opponent such as you describe can send five 3B onslaughts almost simultaneously.

Not many of those who come to the site to shop want to buy burning towns, or CvC "victories" come to that, so the complacent will continue to place faith in their meatwalls for some time to come no doubt.