No.
Is it easy to catch a few bad spawn waves? Yes. Once you realize you've caught some bad waves and they're on top of your spawn is it easy to push them back? Yes. Regroup and use everyone's abilities to push the team out.
is it easy to push them back? No. is it possible to push them back? yes
lets face it, its not easy, the defenders have all the tactical advantage, higher ground, increased visibility, more hiding spots. it is possible however, but takes some coordination and some skill.