That's not right. You query the whole collection unless you pass the param distrib=false.
Very interesting! That's not what I would have expected ... which IMHO violates the principle of least surprise. If the core has the same name as the collection, then it's not a violation of that principle, and from what I understand, a 4.0.0 install does name the cores the same as the collection. I have not actually used 4.0.0 myself.
If cores are going to continue with the 4.1 method of having distinct names from the collection, then I think a request to a core should not go cloud-wide unless you specifically request that with an option.
Users who have never touched Solr before using SolrCloud of course have no expectations about how things work, and probably will appreciate this behavior. It would be a similar situation for experienced users that have never tried the shards parameter.
Users like me that have distributed experience with older versions would be very surprised by this behavior, and will be looking for a "collections" section in the admin UI – which is exactly what happened when I first started working with SolrCloud.