Are #tables and #procedures 'not best practice' or 'bad practice'?
I doubt that the example you provide is a valid use case for temporary procedures (I don't see any benefit here to using #temp procedures over permanent procedures), but for #temp tables, which have a much wider set of use cases, the only way to fight these arguments with policy-setters is to run the code - using a full load and during typical workload activity - without using the #temp tables. If you can demonstrate to them that even one of these processes works worse without the #temp table, then that should be a valid counter. If they still won't listen, then this is not a question for this site - maybe workplace.