I think perhaps you're suggesting a false dichotomy there. Almost any useful general-purpose programming language is going to have both some degree of extensibility and some degree of support from built-in language features. The different flavours are a question of priorities, because the more specialised tools you provide via dedicated language features, the harder it is to keep the core of your language generic. The really successful languages tend to have a set of specialised features powerful enough to give a significant advantage over languages without them, but well enough matched and with clean enough semantics that the overhead for extensibility in other directions isn't prohibitively increased.