Yeah in MP just when you think you have the perfect deck some guy will unleash some obscure unit you haven't heard foiling an offensive.
Unlike so many RTS there's no guaranteed way to win. The tactics are so varied, often down to just the right timing.
At the moment I'm fielding mostly infantry and support units. I love hiding infantry in forests and then walking them to the edge when unsuspecting enemy units move by. Infantry is much improved in ALB.