The explain plan does not show the expression evaluated at HDFS Table Sinks and UNIONs, as well as the final result expressions evaluated at the coordinator. These expression can be very complex. If these complex expression are hidden inside a view (e.g. insert into dst select * from view), it's very hard to tell from the query profile or the plan that the slow HDFS table sink is due complex expressions.
Explain plan should show the expression evaluated at exec nodes and data sinks as well as the final result exprs. Then it would be quite obvious that a slow sink or union is due to these expressions.