I was playing against 2v2 expert AI as portugese. I did the sonic boom to fortress age and boomed up till I got 1200 gold, and hired 5 Samurai. Those guys are like a 5 man army. As long as you don't have them fight artillery or massed light infantry, they will kick serious ass. I attacked the Ottoman AI. and my samurai were slaughtering the jannisaries left and right, and I had 12 cassadores for backup and a indian healer to heal the samurai when they were injured.
But their best attribute is their high siege attack. Its like 150 or so, those 5 samurai destroyed the enemy TC. but I had to sacrafice them. As his British ally sent a mega army of cannons and longbowmen to help him.
That attack on the ottoman kept him from doing much while me and British were at each other's throats. My whole strategy was to mass produce upgraded musketeers and use my 2 factories to make heavy cannons. The game went back and forth quite a lot. They attacked me and destroyed all of my buildings and walls. but I rebuilt and attacked them and destroyed their buildings, then they rebuilt.
Fighting 2 expert ai on expert is really hard. they like to tag team. As soon as you deal a heavy strike to cripple one guy, the other shows up at your base and demolishes your production buildings. I ended up with fast producing infantry, but they still needed a barracks to spawn from, so I built multiple sets of them all over the place, so even when I was attacked, I had other places to build defenders from.
Back to those Samurai, if it wasn't for that crippling attack I did at the beginning. I don't think I would have been able to out produce 2 ai before my economy had matured. the ottoman player didn't make it to imperial for 20 minutes after I did.