You should have one or even both outposts and siege (and the economy to get upgrades at the same time) if Isengard doesn't get Wargriders, but even if there are Wargriders, Knights just mop the floor with them. Isengard can not, under no circumstance, counter Knights until they have pikes - which means that, if used correctly, you'll have the entire map and even a considerable infantry army by the time he has the pikes to stop you from destroying every single external building and unit Isengard has.
Going for Knights vs Isengard in the early game wins you the match, unless you make some terrible mistakes. Isengard does have good pikes, but it takes them too long until they get there.
