Having to use something like array[length] to get the last element demonstrates a defect of that programming language.

There are better programming languages, where you do not need to do what you say.

Some languages, like Ada, have special array attributes for accessing the first and the last elements.

Other languages, like Icon, allow the use of both non-negative indices and of negative indices, where non-negative indices access the array from its first element towards its last element, while negative indices access the array from its last element towards its first element.

I consider that your solution, i.e. using array[length] instead of array[length-1], is much worse. While it scores a point for simplifying this particular expression, it loses points by making other expressions more complex.

There are a lot of better programming languages than the few that due to historical accidents happen to be popular today.

It is sad that the designers of most of the languages that attempt today to replace C and C++ have not done due diligence by studying the history of programming languages before designing a new programming language. Had they done that, they could have avoided repeating the same mistakes of the languages with which they want to compete.