Thank you. Personally I don't like UNIONs too. But these are user queries/views I have to test on SQL 2016 as we are in process of migration from SQL 2008 R2.
Why would it happily work on the same dataset in SQL 2008 but not in SQL 2016?
I can't go and edit all the queries to change Union to alternatives, unless there is a valid reason in SQL 2016 for its poor performance.
In some query outputs Union ALL can cause problem as removing duplicates at an early stage can stop problems elsewhere.