leving both of those commands alone
So a couple of basic questions shake out of this. First, what does the usage (bin/solr create -help) say? Options like -shards, -maxShardsPerNode, -replicationFactor don't apply when creating a core. I think the help should be explicit about cores vs. collections. Second, if the user tries to pass one of the collection specific options (say -shards 10) when Solr is running on cloud mode, I think the script should error out and tell the user that option is only when running in cloud mode. So if you're with me so far, then take a step back, now the 2-modes of Solr are still very much in the forefront of the experience around bin/solr create, which isn't all that different from what we have now with create_core and create_collection, except for the most basic usage of that action, ie.
So if we think there's real benefit to having a "create" alias that's smart about the mode Solr is in, then I'll add it. But I still think the cores vs. collections problem doesn't go away with this create action.