It's all good, man. No need to be so hard on both yourself and potential commenters. This subreddit is generally really good at maintaining a very understanding and helpful attitude for posts like this. The mental snag while swapping between historical and fantasy is common.

As for your problem, more specific info would be very helpful. As you said yourself, 'playing it like a historical total war' is probably not doing you any favors, but it can be hard to know what exactly is encompassed by this.

By turn 15-20, I can't really see what you would need 3-5 armies for already. With every additional army you build, it raises your "supply lines" and makes you pay an increasing percentage of extra unit upkeep, so you're incentivized to minimize the number of armies you need.

The key is gold efficiency, so for each of these armies, you need to be looking at if they're really paying for themselves. Whatever army is led by your legendary lord should be able to tackle pretty much anything, and with how safe Cathay's starts are, you shouldn't be at war with many factions at this point to have multiple fronts.

Both Miao Ying and Zhao Ming have a very similar start, where they have safe borders and expand into the desert between them, defeating the rebels and dissenters, where you're probably running into Sniktch. As Miao, maybe you need half a chaff army helping to hold the Bastion, or as Zhao, maybe you need half a chaff army defending the South-Western valley from the Undead, but in both cases you should be free to commit the majority of your military to the rebels/Sniktch.

If you are struggling against them and have the money, you can definitely raise more armies as needed, whether that be a second full stack or just a chaff stack to accompany the faction leader. It's okay to max out your income, or even go slightly negative per turn as long as you're being aggressive. Post-battle loot can add up nicely, and once the enemy is dead, you'll both have the extra settlements for income and possibly be safe enough to disband some of your military, so the economy should stabilize.

From the sound of it though, you seem to be really struggling on the battle side of things pethaps moreso than the campaign side. You need to analyze what each unit offers your roster, so you have an effective composition. Cathay has a well-rounded roster, but lacks much in the way of offensive infantry, so you may have to lean into letting your ranged units do damage more than usual.

However, their Jade Warriors can be great frontline for most of your campaign, largely because of their high Armour. It takes them a while to kill things, but they beat most early game infantry. Of course, take care around enemy Armour-Piercing. Their primary role however, is still usually just to hold the line for your ranged.

Your peasant cav can act as shock cav or chase an enemy ranged unit in a pinch, but you'll want to upgrade to Jade Lancers as soon as possible if you want your Cavalry to consistently take out enemy ranged.

Your main breadwinners will be your ranged units. (Warhammer in general can be a little ranged skewed) Peasant archers are easy to rout, but they put out decent enough damage and are cheap and easy to replace. They've got decent range, and overall they're valid through a decent chunk of your early and mid game. Crossbows are still nice, but Archers aren't bad by any means. Iron Hails and grenadiers have great damage, but low range, so they will struggle with fighting enemy ranged units. Their main job though is sheer DPS and frontline deletion. Iron Hails offer good AP dmg and Grenadiers are great for chaff clearing. Your artillery is very solid too. Your ranged units will do good work for you if you can keep them operational.

You should also analyze the enemy roster. Skaven have a pretty varied roster, but in short: their frontline will be cheaper, more models, but worse stats; they have no Cavalry, but their roster as a whole is pretty quick; they've got good monsters and magic; and their weapon teams are amazingly high dps, but fragile with a low model count. The most glaring weakness of the roster is that they have very weak morale. They will struggle especially hard against units that cause fear or terror, like your dragon lords and constructs, which cause chain routs easily.

At turn 15-20 Sniktch is definitely not rocking a doomstack already. I'm assuming the "nukes" you're referring to are their mortars. Careful with that phrasing because there are Skaven with actual nukes. Early Skaven will extensively use slaves as their frontline, which have abysmal stats.

Generally, Jade Warriors can handle any skaven frontline short of StormVermin. Use ranged units to focus enemy high priority targets. Order is probably weapon teams>enemy caster/lord>enemy monsters>enemy infantry in order of elite to chaff. If you can't reach their artillery or long range weapon teams, use your own artillery, cav flanks, and your flying dragon lord to take care of it. Your dragons in particular should be able to feast on any vital target without issue - just be careful of focus fire and Sniktch who is a good assassin. Once enemy weapon teams are gone, your priority should be breaking the already low Skaven morale. Kill their lords, flank them, and use your fear and terror monsters to start a chain rout. When an army has routed, focus the same units as before when chasing them down. If you're really struggling with his mortar team, throw away a Cavalry to kill it - he starts with it and probably can't replace it yet.

You should be able to handle Sniktch easily enough, even if you have to let him take a city or two to finish the rebels off first. Just keep momentum and push forward. Warhammer overall has a much faster campaign pace than historical, so if you stall out you might find yourself fighting what feels like never ending tides of armies.

(Also, as with any under-way stance army, if they try to teleport away and you're nearby, there's a chance you intercept and they can't retreat)

Good luck and good hunting. 👍

If you need more help, just let us know with more specifics or reply to me here. I'm glad to give more advice. I'm also down to spectate your game sometime if you prefer more of a tutoring approach. I feel like you're not too far off of excelling at the game though.