Re: 2,500 systems?
Decent sized store.
Rack A, maybe 4 or 5 42-47 U racks that are filled. Some SAP servers (plus redundancy backups), various other servers for things like muzac, ads, loss prevention systems, CC, IOT stuff etc. Shitload of switches. Rack B checkout switches (all doubled up for redundancy), couple more racks dotted round the store mainly switch racks again (also doubled up) for other checkouts, scales, AP, stuff like that.
It adds up.
I've worked with ASDA when they were Walmart owned. Walmart's actual IT infrastructure is huge they also had some highly skilled network engineers etc there. They took their IT infrastructure very seriously as down time was measured in tens of thousands of dollars per hr at large stores. God forbid you needed to do work at a store during certain seasons - it would only have been mission critical stuff like a dead switch, the managers would be actively hostile to people trying to do the work at this period (whereas they usually were accommodating for the most part) and the change controls to do the work got bumped up several layers of management for review.
The IT overhead for a large supermarket chain is actually pretty big, LIDL have recently started selling their services as a datacentre - they probably didn't need to scale the teams, skills. or hardware up much.