Rivera has played well in the time he has got here. Its ok to think hes a AAAA but if he is in the middle of a good run then play him. Its not like the offense is doing much anyway and he is supposed to have a good glove at 3b
The only reason that Holliday is playing against a lefty is because Mountcastle is unavailable. You'll see Rivera at third and Urias at short more once he comes back. Holiday has looked especially overmatched against lefties.