One can only imagine the hike from the bottom to the summit (or should that be "pass") would have involved rather a lot of "Remutaka" stops.
Over generations, bastardisations of words and language occur.
English is a constantly evolving language, and as much as every generation fights the change, the upcoming generation usually adds and adapts it.
But the Maori language, which is "young" if compared with European languages, is far more vulnerable to bad and lazy pronunciation, which many of us are guilty of.
It could well be that Rimutaka is a result of that.
In its written form, we're guided by macrons to indicate long vowels, and I admit I wouldn't have known that it's Ruamaahanga in spoken form, without that guide. But we live in a community that still says "Cow-haut-tra" for Kahutara, and that makes me cringe.
Newspapers are frequently told to correct errors of fact. If the closest, most precise written word and pronunciation for that winding road to Wellington is Remutaka, then correcting an error of history is worthy too. It is an arrogance to think ourselves aloof to correcting mistakes.