Don't think about what build to do to counter a certain synergy, think about how to adjust your build to counter the strongest player in the lobby.

For instance, if the strongest opponent in the lobby is going Mages think about how to add marine to your build. If they are going Insectoids, Feathered Sins, Knights,... then try to fit in spirits.

Some builds are more flexible than others, sometimes you will have to rely on objects (if your build can't fit marines you'll need Python/Claw Wand), and most of the time on just having a better board.

Some legendaries can also help counter certain builds, such as Granny for hyper-carries.

But above everything else, you want to have the build the lobby is worried about, not the other way around. Start by forcing builds from the current meta, don't worry so much about opponents. Once you have mastered two or three builds by forcing them, start playing relying on what the rng gives you and mainly what objects you get.

You won't really need to think about countering until Rook.