As I look to go on the offense soon I'd like to make an argument about the strength of chokonus and why they're an A tier uu. Let's say you're up against typical AI build, so 3 defenders in each city + a 10 stack somewhere, we'll say in his capital a few tiles away. How many units do you need to commit if you want to safely take the capital, say at least 90% odds? This is a tricky question, as in the time it takes for your units to move to the city and then barrage defenses he could reinforce a couple units. My answer is about 20 units. But the siege number is important too. If there's too few siege, you'll have to spend even more turns barraging, and there's more time for surprise reinforcements. If there's too many siege, a bad dice roll or surprise reinforcements can mean you don't have enough non-siege units to kill every defender. My answer is 13/7 or 14/6.
Now if we ask the question of a chokonu army, I'd answer 14 units total. And there's the added flexibility not needing to worry about the unit composition (sans a spearmen defender if they have horses). You won't find yourself in a situation where you burn turns waiting for siege to catch up. This flexibility also means it's much easier to split your army into multiple stacks, without worrying about maintaining a siege ratio, having to escort defenseless siege, etc. So with those same 20 units, I can send 6 choks to go attack one of the periphery cities with the minimum 3 city defenders. This just isn't possible if you're relying on siege. We might not need siege collateral, but we need to barrage defenses. You'd need like 12 units to go after this tiny 3-defender town efficiently, or like 9 non-siege if you don't care about taking heavy losses. If your army is mostly G3 choks, the small portion you use on the periphery cities may even be able to act as two-movers depending on hills. The end result is 20 choks are taking TWO cities down faster than 20 standard composition troops are taking down one. The downside is the espionage cost. However, medieval war almost always taxes the player's economy to the point of being behind. EE is well suited to play catch-up, while your traditional beakers/bulbing either slingshots ahead with breakthrough techs and trading, or it falls behind. The infrastructure for an EE (namely TGW) generally carries the opportunity cost of fewer, worse cities. But we don't really need a strong core to keep the Chokonu wheels grinding. The high withdrawal chance means we can keep growing an army while at war with a pitiful empire that would otherwise struggle just to replenish the suicide siege.