Okay, let me stop you there. 3K is a bit of a different beast with larger Rare allotment and slots, rather convenient in terms of adding up monsters. You can take more monsters, but you can expect to see up to 4 ironblasters or 6 cannons out there. That is not what I would consider a "standard" game. But you keep putting ridden monsters in there. That means putting your general/level 4 on a big monster and hoping that when the cannons blow him away, your other rare monsters will make it across. Well, maybe they will, but you've sacrificed your general and/or level 4 to do this! Few armies can take hero-mounted ridden monsters and even then, they represent a huge points sink for what is essentially a cannon-magnet. Sacrificing 600 points to allow 400 points to get across the board maybe doesn't seem a good deal.
Furthermore, people don't do this, at least not competitively. Beastmen can fit quite a few monsters but I've seen very few on the tables.
In my area, 2.5k and 3k are the common field sizes. On average you need to have the same amount of points in Artillery to deal with an equal amount of points of Monsters. If 1 out-classes the other that will more than likely survive. Thus if you have 200 points of cannons but I have 600 points of Monsters, I'm getting 2 of my monsters down the field. But if you have 500 points of artillery and I only have 400 points of monsters, then my monsters will disappear.
That's fair enough and these days when every army is getting support units behind their lines (mortis engines, corpse carts, wizardmobiles) will put pressure on cannon target priority. Like I said before, I take a terrorgheist in my VC because enemy cannons are hard pressed to deal with it and if it dies then my mortis engines and corpse carts aren't getting targeted. But don't include spider riders, manglers and even giants in the category of being target saturation for cannons because they can be dealt with using other units. Handguns aren't a big threat to a proper T6 monster so that's where cannons come in, but you don't need a cannon to kill a mangler. Typically I'll have other things to deal with secondary threats like this and if you put a wyvern on the board I won't be scratching my head wondering what I should be shooting my cannon at, I can get a massive points return for blowing it away, nuke your general, or I could shoot at a 65 point mangler my handgunners can deal with?
Mangler squigs are extremely hard to deal with outside of a gunline. I have seen cannons used against them. 2 Giants, 2 Squigs (2250 list) I include Spider Riders and my hero as well. It's target saturation. Outside of a PURE GUNLINE you will Not have enough shooting/magic to deal with:
2 Giants, 1 Wyvern, 2 Squigs, 2-4 units Spider Riders, 1 Goblin Hero on Giant Spider, SO Boar Boyz, Squig Hoppers. All of that is Turn 2 charging. You may kill the wyvern and maybe even the rider on top. You may kill both squigs. But then I repay the favor by taking your handgunners and artillery. Then it comes down to what is the rest of our army made of

Just like chess we'd equally trade.
A single monster is a liability. A list built to sustain monsters is suddenly fearsome. Fortune favors the bold. When you build a monster list you have to go all or nothing. A smattering of Monsters and speed will be quickly countered. An entire list of Speed and Monsters is not

If you want, send me the point totals you'd want to play. You create a balanced tournament list for whatever point totals and I'll send you a list of a monster mash that I take to tournaments. Mind you, my W/L is usually extremely high with Monster mash. Yes, sometimes I get unlucky and I go up against that 1 player who brought an all shooting dwarven gunline and I get decimated. Then I laugh because I could just see dwarves ambushing the monsters.
Agreed. But that means the enemy can focus cannons on other targets. Bringing two giants isn't going to keep the cannons off your wyvern!
Exactly, but bringing 2 Squigs, 1 Goblin Hero on Giant Spider, Spider Riders, Boar Boyz, Squig hoppers will

And even if my wyvern/lord dies (he's not my general) thats a fine trade for me! I'd rather my giants hit their line, they do more Damage per Turn on average than the lord on Wyvern
I don't mind it not being realistic. I object to the argument that killing characters off mounted monsters is fine because it's supposedly realistic, when it isn't realistic to be hit in the first place. If we agree it isn't realistic, then the only argument is that it is required for game balance, which seem patently absurd.
And I do not wish to change your opinion. I'm simply arguing on the monsters sake, that cannons are fine and if nerfed we'll be way too powerful.
Eh, it was one of the most disappointing aspects of 8th for me. Ridden monsters really weren't taken that often in 7th. Then 8th comes around, with the % system still making it hard to fit a level 4 and a general on a monster in the army, for some reason taking cannons and making them more accurate and hitting both rider and mount was required. How did they not realise that would make ridden monsters almost extinct?