The number of ways to write something is only very loosely correlated with maintainability. The ease of maintenance is IMHO more a function of how much information about the properties of the code you can easily read from the text, and how well the abstractions in the code map to the abstractions you'd use when describing the solution to a friend. Lack of features doesn't help in that regard. That's why probably Go has just added generics, despite the long tradition of Go promoters claiming "lack of generics is a good thing" ;)
Languages with very little type information, e.g. dynamic ones, tend to be quite hard to maintain, unless the original developers kept the discipline of good naming and verbose commenting. Go and Java with their somewhat static, but limited typing and elements of dynamism (interface{}, Object, reflection), sit somewhere in the middle between PHP/JS and Rust/Scala/Haskell.
Languages with little expressive / abstraction power, so the ones limited in features or low-level are also often hard to maintain, because you have to reverse-engineer the high-level stuff from all the details you see. Take assembly as an example - while it may be quite obvious what the program is doing at the bits and bytes level, understanding the sense of that bit-level manipulation may be a much harder task. The assembly language might actually be very simple, but that does not help. I remember when we had a MIPS class, the whole specs was just a few pages, could be learned in an hour.
Languages with very little type information, e.g. dynamic ones, tend to be quite hard to maintain, unless the original developers kept the discipline of good naming and verbose commenting. Go and Java with their somewhat static, but limited typing and elements of dynamism (interface{}, Object, reflection), sit somewhere in the middle between PHP/JS and Rust/Scala/Haskell.
Languages with little expressive / abstraction power, so the ones limited in features or low-level are also often hard to maintain, because you have to reverse-engineer the high-level stuff from all the details you see. Take assembly as an example - while it may be quite obvious what the program is doing at the bits and bytes level, understanding the sense of that bit-level manipulation may be a much harder task. The assembly language might actually be very simple, but that does not help. I remember when we had a MIPS class, the whole specs was just a few pages, could be learned in an hour.