I know how you feel, sounds like most of my experiences with large-map games
There will probably be some advice coming from more experienced players, but what I can say is you'll have to work on the magic strategy a little. Taking down armies that have you massively outnumbered with poor troops can seem just about impossible, but a little of the right magic, properly applied, makes it easy.
With Ulm, the most important spell will be blade wind. It's an earth spell, and L6 Evocation I think. So you need the research to cast it, and boosted master smiths... I think you only need one booster level to cast it, but it's an exhausting spell to cast, so antifatigue items and even more earth boosters will help immensely. You want the spell summon earth power, that's IIRC conjuration 3, cast that the first round and it boosts your mages earth level 1 point for the rest of the battle. With summon earth power alone, they should be able to cast it, add some earth boots and they can do it without passing out

It's not very good against anything with heavy armour, but will cut a nice huge swath of lightly armoured troops down with each cast.
If you're playing Ulm you also want to really work on construction. You need construction 4 for your master smiths to make dwarven hammers. Between their natural forge bonus and the hammers, you can churn out a huge number of useful items for the gems. All your battle-smiths should have earth boots and the anti-fatigue girdles ASAP, for reasons above. Once that's accomplished there are all sorts of other wonderful things your forges can churn out too. So basically what you want to research is construction 4, evocation 6, conjuration 3, not necessarily in that order, but all three of them as soon as possible. That gives you the tools to swat down enourmous hordes of crap troops like the insects they are
Ulmish arbalesters are powerful missile troops against heavily armoured enemies, but they just aren't cost effective facing hordes of cheap crap. For that you have to rely on your mages.