I'm having a great deal of trouble with the "Rescue O'neron"
desert scenario. I've got the difficulty level as low as it
can go, and I'm barely able to escape any of these scenarios with
my life.

The enemy Tigran units are so Overly Powered that it throws
the game out of balance. The Sphinx and Manticore are
ridiculously powerful, and are produced in quantities that the economics would not seem
to be able to support. My own cities are maxed out producing
goods, and I can barely keep from going broke supporting just a fraction of
these enemy armies.

The worst aspect of the game is the Pestilance Cloud.
It's one thing for this to do some damage, but it also freezes
the units in place. I'm not a robot. I find it boring, tedious and
stupid to have to move every single unit individually, so I build
stacks. Then they get hit with a Pestillance Cloud, the enemy
renews it turn after turn....in complete defiance of reality.
There is no mathematical way the enemy has that much
Mana to spare.

I'm also discovering that my own units just spontaneously
surrender the moment an enemy stack touches them. What's
up with that?

Finally, the economics of the game mean that you have to
sit there for something like three thousand turns to build up.
Guess what, designers, this is the OPPOSITE of "fun".
Grinding, crushing, boring, tedious....work, work, work.
A game that will suck the soul out of you and flush it down the
toilet.

This game WEEPS for cheats, and lots of them. Agonizingly
hard! Where are the cheat codes, please? Thank you.

Assuming you're talking about the original game...

I'll have to agree that it seems the game 'cheats' with the economy of the AI races. I recall playing one scenario where I had managed to outmaneuver the AI at most every turn, had at least twice as many cities and mines for most of the game, had about the same number of armies and support costs, yet the graphs after victory showed that the AI had almost 4,000 gold at the end of the game and I had a couple hundred. Ditto mana, where he was casting (and paying upkeep on) Enchanted Weapon for about half his units while I was barely scratching by for just half a dozen units.

Keep in mind, though, that there are some spells that boost city income. Use the magic tab to see if that's what's going on, and then try to dispel those enchantments.

On the plus side, you can make up for some of the cheating by taking advantage of the AI incompetence with regards to cities with walls. If it has a wall and one unit in it, odds are you're safe from attack unless he builds some wall-climbing units; at least that's what I've found in the early portion of the campaign.

On the surrender problem, maybe you're stuck with low morale in your units. Are you building units from the enemy races?

This is actually one of the easier missions imo.

I dont want to spoiler the mission, so I will say you are approaching the mission the wrong way. Check your quests, complete the quest given at the start of the mission to complete it.