I understand your complaints. However, despite deprecation, I can use Triple DES as a choice for the DEK. It's valid on a SQL Server 2016 instance. There's nothing in the question about compatibility level for the database. A database on a SQL Server 2016 instance is not required to be on any particular level.
I'm not sure I think that I need to specify the compatibility level for every database as well, but maybe that's the case. I would say that you're making a leap about what options are valid on SQL 2016 and extending that to assume the database is always at the level of the instance.
I agree with Steve on this. On the instances I have had the joy to administer over the years, compatibility level lower than the instance version number is more a rule than an exception, because most companies try to consolidate databases. 3rd party systems most often don't support the latest Sql Server version.
Sql Server blog: http://www.tsql.nu