What is the antonym to ‘minimalist’?

There was the following sentence in New York Times (May 26) article titled, “No real hurry to tell the joke -Bob Newhart, Master of the one-sided conversation”

Bob Newhart has always been a gentle minimalist, which may be why he does not get anywhere near the critical respect of fellow founding fathers of modern stand-up, like Bill Cosby or Lenny Bruce. http://www.nytimes.com/2014/05/27/arts/television/bob-newhart-master-of-the-one-sided-conversation.html?src=dayp

Is there one word antonym to ‘minimalist’? If not, what is the shortest antonym to ‘minimalist’?

Sticking to the context you’ve given, we might say that radically non-minimalist comedians have an in-your-face or over-the-top style. This would probably apply to Lenny Bruce, but not to Bill Cosby. I’m sure there is a more succinct way to express this, however.

A more general antonym is baroque (but not for comedians.)

One antonym of minimalist is profligate.

As a noun, profligate means "a wildly extravagant or self-indulgent person". The word profligate is also an adjective (similar to minimalist), meaning "wildly extravagant". An alternate adjective is prodigal.

Incidentally, the word maximalist is not actually an antonym of minimalist; on the contrary, it is political jargon meaning "one who advocates immediate and direct action to secure the whole of a program or set of goals".