Winter level completely impossible for Zombies

That first point was a nightmare at launch but it's been made easier due to a few reasons including the Rose changes, pot placement, and others. As a zombie I tend to have more success with flanking and running from cover to cover and either building or supporting the building of a teleporter and defensive bots.

I certainly don't find it trivial to take as the zombies but it is certainly doable and I generally win as the zombies if we get to the final point to free the yeti king.

Defense is generally easier in these games since the attacker must take the points which channels them into a particular area whereas the defenders merely have to keep the attackers off the point. Once attackers are one the point defenders need to get there to stop the capture process but if they can keep the attackers off that point in the first place they can dig in and force the attacker to play their game.