I find the game ridiculously hard even on easy setting. Simple as that.

I understand that the OP is quite old. But playing FW right now, I would like to chime in anyway.
I'm playing on medium difficulty (the default setting) and the game is hard but not insanely so. As usual the AI is not very challenging and makes some interesting mistakes quite frequently (e.g. not attacking units in front of a city wall or ending movement in a river.) Actually this is laudable. The AI does not cheat, there are no surprise reinforcements (switch of the Fog of War to convince youself), there are no hidden boni and the AI works to the best of its capabilities, which, like always, isn't that great.

The designers compensated by giving the computer superior numbers and better quality units. So, business as usual. The typical counter measures are effective (keep you troops together, concentrate your firepower, employ diverse tactics.) What is annoying is that the designers decided to move the goalpost on a few missions, i. e. you fullfill your mission objective and through a narration the mission is expanded, making you miss the gold level. But that's really all.

I enjoy the game.

The game is just as hard as a good strategy game should be. When you are new it is difficult, after the learning phase it is normal and when you have played the game as much as me it is easy.

If you play on normal...a few mistakes or silvervictorys are allowed and it wan't be to hard but faults accumulate.
Start with normal difficulty, play the first 2 or 3 mission, replay them if you don't reach a goldv...if you aren't able to reach a goldv. during the replay...play on easy.

Anyway..if you're at least medicore at tactic strategy...you should have no problems to beat the game.

I enjoy this game but the missions have been designed to be completed in a very specific order. Finding what that is takes trial and error. Thus, you'll find yourself replaying missions over and over.

I eventually lost interest when every mission put my small army against an enemy 3x my size and with superior units.

That is not true at all, most missions can be completed in 2-3 different ways, not to mention the different unit types you can use. Then you can also decide if you want to clean the whole map or go for gold.
After playing through the game like 10 times, I can assure you that it is no problem to get gold in hard mode in all missions with different methods.
But if you don't want to gold as some sort of special goal, it can be much better to do the entire map in the first missions to get experience for your units instead of getting the gold and silver rewards.