Why isn't it a full groupset? what am I missing?
Chainset and brakes would normally complete the groupset except where disc brakes are spec'd so the Synapse is only really a chainset short of a full groupset.
This is partly what makes many Planet X bikes good value as you often get the full groupset at a lower price point. At the reduced price though, the Synapse is good value too and being your first road bike you probably wouldn't tell the difference between an FSA and 105 chainset.