Yes, 802.15.4 S1 modules do not support mesh networking. So they can be used to form star network.
If you going for S2 modules then networking will definitely be more complex compare to star topology. But it is something that modules will handle at their own level and figure out best route for transmission.
From user’s point of view, both S1 and S2 will look equal if we are exclusively talking on networking routes complexity.