a word for functionalism as decoration

gewgaw, as defined by Wiktionary

Showy; unreal; pretentious.

It has a nice 600 year history, too. 1678, Dryden, John, All for Love, Scene II,

The rattle of a globe to play withal, This gewgaw world, and put him cheaply off.

Another example: 1855, Alfred, Lord Tennyson, Maud; A Monodrama, X, stanza 1,

Seeing his gewgaw castle shine, New as his title, built last year.