In this case, I disagree. Most Highways and REoutes around me are spelled with a number an dnot the word, and Route 2 would fall under that. Tehexcaptions beig Tenth Street,but Instarste 5 or I-5 is alsways Insterstate 5, not I-Five.
You're probably right. Since the routes in Unova are the actual names of the area, it's probably best to leave them as numerals. But in other instances when using quantities, it's always best to spell out numbers unless they're redonkulously long (I forget the rule)