I scoured through the Topstone geometry (i'm considering buying one) and i can find essentially nothing in common with the Synapse.
It's more the fact that while the Topstone geometry is closer to a CAADX (especially the head angle and fork rake), It very much aim to a similar crowd as the Synapse alu.
I am glad that it loses the huge headtube of the equivalent synapse though, i had a synapse as a winter bike once and while it was actually quite good in terms of discs / guards etc i never really got on with the geo and it gave me knee pain regardless of how i set it up
It's more the fact that while the Topstone geometry is closer to a CAADX (especially the head angle and fork rake), It very much aim to a similar crowd as the Synapse alu.