Edit: I mean makes it bad to use for a normal non horde army. Malakai is really the only one who can counter attack north, and even then you dont have much incentive to do so. Clearing enemies just lead to you meeting new enemies and its a cycle that slows you to a crawl

Malakais campaign is my most recent campaign and I is fine as he snowballs hard and fast but has a somewhat challenging early game. everything you mention about enemies on all sides is true and no you should not bother venturing north. make walls for garrison. fight your battles and use a 2nd lord with a small garrison to help settlements hold off forces. I quickly took out Kholek and surrounding enemies with Malakai and chaos is very weak to gyrocoptors and artillery and slayers have great replenishment rate and will hold the line. When you hit your age of reckoning and get a free army you have basically won. Just remember to focus down one enemy at a time and if you need extra armies you can use diplomacy to join other wars with people on the other side of the map for cash who are never going to bother you.
Age of reckoning units on tap to recruit in an emergency are OP, get a horde of chaos warriors in a defensive battle to blob up and kill them with iron drakes flamethrowers you recruited a turn ago. Once you have enough rune gold get the rune of spite asap on a demon slayer lord with an ironwarden tankard and watch your enemies army melt. I swapped the rune out to a new lord each turn and had a lv 1 demon slayer kill a fully maxed out garrison and capture a settlement in a manual battle.