It's impossible to defend in breakthrough.

In that case, play Breakthrough on Exposure.

There, attackers never win (well, almost never if the defenders are at least somewhat competent).

But independent of which side is favored by bad game design decisions: those one sided matches are rarely/never fun. Neither for the winning and especially not for the losing team.

I played a game last night as defender and the team was an absolute fortress.  AA was good.  Vehicles were getting Soflam and destroyed.  Attackers couldn't push through.  Had the hill covered and the flanks. They must have been hating it.  They only challenged the first sector maybe 2 or 3 times and were taken out within a matter of seconds. 

Wish we had persistent Servers as would have been good to see if that was a true fluke and whether the attackers would have learned anything in following attempts.

The reason is because most of the time the defending Team is to stupid to understand that they actually have to stay on the Point they want to defend and not waiting around it while it's getting captured 

Keep your squad in or very close to the capture/defend area.  Pay attention to all entrances to this area.  Use proximity gadgets and Paik who is an excellent defensive specialist to spot check the capture/defend zone.  Having a squad mate that throws out ammo always helps as well, but to say defending is impossible is just not true.  

It is the way that a lot of people go about defending that is causing them to lose so often.  If the capture/defend area is indoors then there are no excuses.  There is always a sector on the map that gives defenders an advantage if they are smart enough to take advantage of it.