Uneven surfaces are easier to handle for larger landing craft, since the variation is proportionally smaller compared to the vehicle itself. A Falcon 9 booster requires a pretty much flat surface, a Starship should be able to handle as much as a couple meters of variation. If you need to land a vehicle that's less capable, you can land something else first and prepare a landing site for it.
You've brought up launch clamps before. It isn't clear to me why you think they're necessary. SpaceX has done several flights of Grasshopper vehicles and Starship prototypes with no launch clamps.
Splitting a vehicle into a mothership and subcraft has numerous downsides:
- Subcraft and motherships require you to develop, build, and operate two vehicle types instead of one.
- Subcraft are dead weight the mothership must haul around for much of the trip.
- Subcraft represent dry mass that must shuttle back and forth to deliver payloads to/from the mothership. If they must make multiple trips, this can add greatly to the propellant requirements.
- The mothership must stop in orbit at the destination. It is possible for this to be done with aerocapture, but this requires much more precision in atmospheric braking than simple entry and landing does, and also requires the mothership to have most of the thermal protection and aerodynamic features it would need to land. It is likely you will burn more propellant getting the mothership into orbit than you would landing it.
- The penalties of reuse are proportionally larger for smaller vehicles. Things like heat shielding will be a larger part of the overall mass budget. Gauge issues mean there will be more structural overhead for smaller craft. For example, directly scaling down sheet metal components might lead to the sheet metal being impractical to build with, requiring you to use heavier sheet metal than would theoretically be necessary.
There may be an argument for such a split if the mothership is of extremely large size (far larger than Starship) and makes use of exotic propulsion systems not compatible with landing (such as nuclear-electric propulsion), but the advantages will have to outweigh the numerous disadvantages, and such a vehicle isn't going to be a replacement for Starship.