Hello,
to answer your questions:
- SAP SLC is definetely better for supplier enablement and performance management compared to SAP SRM and Sourcing.
- SAP SRM can be sufficient for the strategic procurement processes, however SAP Sourcing is more extensive.
- SAP Sourcing is definetely the best-of-breed when it comes to contract compliance.
If you want to cover the entire purchasing flow, you should go for the three different solutions. However, if strategic sourcing requirements are simple/standard processes, you can also choose SRM alone. If requirements are very explicit and detailed, you should definetely opt for Sourcing on top of SRM.
Bram