It's really unclear documentation isn't it.
From this old post by Diethard Steiner http://diethardsteiner.blogspot.com/2013/03/creating-clustered-transformation-in.html it looks like a cluster schema needs to be set up as well - which you can only do from a transformation (weird?)
Another reference is here https://pentaho-community.atlassian.net/wiki/spaces/EAI/pages/374571420/Dynamic+clusters . Also quite old but it does look like the cluster schema is very important.
Since you haven't mentioned that step and the 8.2 documentation says it is for executing in parallel you might have missed it? But it also says
If checked, a master Carte server will perform failover operations, and you must define the master as a slave server in the field below. If unchecked, the PDI client will act as the master server, and you must define the available Carte slaves in the field below.
Man, what a cluster-**** : D