Well, this is Warhammer, so every unit is basically the bestest in the world (narrator: they aren’t). And some units are really not worth their cost in Gold - the White Lions is one of them. Units with low defense and HP tend to suffer - it doesn’t help that you can kill enemy units fast,
Different players will have different playstyles, but my go to strategy, which works for many races, is to build lots of low-level spearmen (8-10) and archers (8) in the beginning, at least for the first 1-2 armies. You want to weaken the enemy as they advance, then allow them to engage your spearwall in combat (which is why this strategy usually uses spearmen rather than swords - spears die slower, though a mix can also work), then use your few starting elite units to smash the enemy morale by charging the enemy in the flanks/rear. Ideally you also have some starting artillery, which will usually force the enemy to come to you (rather than the opposite) - that’s always a big help. Upgrading to shielded spearmen/swordmen if possible is an advantage, because it again allows them to survive a little longer (and especially make them less vulnerable to enemy missiles), but I’d rather build up to a full army before upgrading the buildings.
Your lord’s task (if he is any good), is to take out the enemy leader/hero if he can. That both makes it more likely the enemy will break, as well as rids you of one of the enemy’s dangerous units. Dragons (and flying melee units in general) are there to destroy enemy missile troops/artillery first, distracting enemy melee units, and then to join in charging enemies from the rear once any missile troops have been dispatched.
The Lothern Sea Guard is brilliant because it is basically Shielded Missile Unit with spears, which means they don’t need anyone protecting them, so you can pretty much run with 1 Lord, 1 Artillery, and 18 Lothern Sea Guard if you feel like. It’s a formidable (though weak to heavily armored enemy), if a bit boring, army.