LISTAGG (measure_expr [, 'delimiter_expr']) WITHIN GROUP (order_by_clause) [OVER query_partition_clause]
SQL Server's listagg is similar to the PG implementation. It seems Oracle thinks people would prefer to order the list and for that reason, made their listagg a rank function type. Having done quite a bit of work generating delimited lists/arrays based on ordering in PG, I generally agree that it's what I would generally want.