The new data model was switched/based on column store vs row store. S/4 was placed on top of HANA for Enterprise Information management.
Gone are the complex model as of HANA 2.0.
HANA does in memory computing. Good bye Index and aggregation management as it is done on the fly.
Simple in short: - The switch from row base to column base tables is the key. Still use row in some situation but the new design along with in memory index tables and allow for on the fly aggregation.