Now imagine that you are fighting a German opponent who will go FF and straight to Mercenaries with support units. Or that you're fighting a Spanish opponent who'll FF for Lancers, Skirmishers, Falconets, perhaps Highlanders if he wishes to delay the attack abit and ofcourse the horde 'o Pikemen.
Now think about this, if you ship Manchu, and you wipe out the Spaniard's Lancers, how useful will these Manchu be afterwards against the Skirmishers, Pikemen and Falconets? Or how about if the Spaniard builds Dragoons? Or even worse, Let's consider the German opponent. He'll likely come at you with: Against how many of these units will Manchu excell? Uhlans. That's it. That's Even if, whether you're fighting the Spanish or the German opponent, you back these Manchu up with Falconets, they stil perform very poorly for their cost. And let's assume you won the engagement. What do you do with the Manchu now? Let 'em sit around getting fat? They make poor raiders, what with them being cavalry (extra TC/Outpost damage) and having that annoying 0.5x multiplier vs villagers. ... But let's say you sent 11 Corsairs instead. After Corsairs go through the Lancers like a hot knife through butter, they are actually useful against the remaining units! Now let's say you won the engagement. What to do with those left over Corsairs? Go raid with them. With their speed, villagers just don't get away. And their hand attack is almost as good as a Hussar's (28 vs 30). Oh, right, that German also had Uhlans and Skirmishers with him. Well, we know what happens to those when you send Corsairs and Falconets at 'em, right? ~~~ Now, you might be thinking, hell man, I'm Portuguese (for example). I can ship in 6 Dragoons to deal with those Lancers. I don't need no stinking Corsairs! Well, consider just how well your Dragoons will perform against the Pikemen, Rodeleros and Skirmishers (not to mention Highlanders!) after you killed the Lancers? So you can take this train of thought from here. Like I said, once you begin to seriously consider the implications, this is only the start ...
Not very useful ofcourse, as Manchu don't do all that well against these units, units that aren't melee cavalry. Yet you've sunk a Fortress shipment and 1200 gold into these units.
Black Riders
Jaegers
Skirmishers
Uhlans
(and some time later, when he builds 'em) Falconets.
Jaegers and Skirmishers also hurt Manchu quite badly.
Stil, you've invested 1200 gold and a Fortress shipment.
If they close, they kill Skirmishers, Pikemen, Rodeleros (their inferior cousins) and Falconets.
And Dragoons? Oh my, there is little more satisfying than watching Corsairs cut into a group of Dragoons, before they can get away.
The only trouble the Corsairs will get from is ofcourse the Highlanders. This necessitates Falconet (and Abus Guns if you're Ottoman) support. But, ofcourse, you'd have Falconets most of the time anyway. You don't rely on a single unit in the hope of winning, right ... right? And you're probably going to have a bunch of other units there as well, like Cassadors or Spahi. But Corsairs will be key.
Now let's consider the German opponent. His Black Riders can hit and run every single Corsair to death, normally. But not if they wish to protect the Jaegers.
If Black Riders run, your Falconets and Corsairs finish off the Jaegers that much faster. If Black Riders stay, they get annihilated by the Corsairs. Just make sure to micro those Falconets of yours well. Don't have 'em hitting houses or the Black Riders. Concentrate on the Jaegers, and make sure you target such as to catch as many of them with splash as possible.
Right, not so well ... but you just spent a shipment worth 1000 resources on those now barely useful units.
"One wants to be loved, failing that admired, failing that feared, failing that hated and despised. One wants to instill in other people some form of emotion. The soul shudders before emptiness and wants contact, no matter the cost."