So why does it take 5-10 seconds from card presented to accepted at Starbucks and CVS?

Usually the dominant time is from POS to acceptor. These are frequently still on high latency links.

Also a lot of times in person payment flows allow a lot more in their latency budget because it won’t impact the sale, you won’t walk out because of a second here or there, unlike online.

So systems aren’t as optimized, they route to older systems, marketing or further risk checks are added, and a broader range of accepted services that have higher latency (ent/snap processors and the like).

This scenario does not include payment. Would be much more interesting if it did.