I agree that you can write with just a subset of the language. But the problem arrises when you have to read somebody else's code.
If there are too many features as opposed to "one and only one way to do it" you will end up with a source code that is unintelligible between two developers.
Imagine it has M+N features that are mutually replaceable. The problem arises when you have a very good programmer that writes a complete program using the M features, and when you get programmer b who is also good but hasn't heard of the M features.