He took our infirmities is Matthew’s caption over healings, not over a later political Israel.
Isaiah’s Servant is despised, pierced, and makes many righteous. The Gospels put that life on one Man.
Matthew 8 quotes Isaiah 53 over sick bodies. Matthew 20 and 26 put the same Servant on the road to a ransom-death.
The apostolic generation preached a Servant already exalted. AD 70 did not create that fulfillment; it exposed those who refused it.
The Servant has finished the work. New Creation healing is participation in that finished wound, not a wait for another Servant.