now that we no longer send passthrough commands to shards for unsharded collections, they have to get parsed anyway. Now the only savings we get from this deferred parsing https://github.com/mongodb/mongo/blob/e1139aebc374b0b84e3243d23cd2c65c43acfc8a/src/mongo/s/query/planner/cluster_aggregation_planner.cpp#L771 is that it speeds up the initial agg for $_internalPassthrough to shard (not common) and situations where we would throw the tassert.