You are correct in observing that a new covenent was being put into place.
Please do not think that God cannot and will not make new Covenents with his people. We see this throughout the Old testament.
If God had not made the new covenent after the flood, we would still be vegetarians and the animals would not fear us.
If God had not made the new covenent with Abraham , the Israelites would not have come to pass, at least through Abraham.
Now, bact to the new covenent with the Apostles. We are now to celebrate communion rather than passover. THe reason for this is that we no longer need a perfect sacrifice, Jesus is the lamb and he spilt his blood so that we would no longer have to spill the blood of innocent animals for the covering of our sins.
Jesus Christ was and is the perfect sacrifice and to deny that is to deny what God told us from Genesis onward, that he would send the perfect lamb, to free us all from our sins, not just the bondage to the Roman Empire (which is pretty short sighted, considering God is much more powerful than one little empire)