We've back and forth over handling maxShardsPerNode with autoscaling policies (see
SOLR-11005 for history). Now that we've reimplemented support for creating collections with maxShardsPerNode when autoscaling policy is enabled, we should re-look at how it is implemented.
I propose that we fold maxShardsPerNode (if specified) to a collection level policy that overrides the corresponding default in cluster policy (see SOLR-12845). We'll need to ensure that if maxShardsPerNode is specified then the user sees neither violations nor corresponding suggestions because of the default cluster policy.