What was the point of it
Because they're building Kalisto as an underdog.
A core part of what makes an underdog is sympathy with the fans.
He finally climbs atop the spire, he gets the crafty win over the vet, he becomes US Champ, he promptly gets his ass kicked back off of it.
They're likely gonna continue the feud through to Wrestlemania with Del Rio just whooping his ass until he gets his retribution and they attempt to firm Kalisto as a new Mexican star.