'Gateway to ...' is a metaphor / cliché. The sort of thing that was often used in the past as a marketing tool. I can kind of see why you could describe Crewe as a gateway to the Northwest - as long as you assume travel from London (by train). But it doesn't mean that there is any benefit in doing so. And as a lot of the comments above suggest, there is very little value in attributing it that way now that we have accepted that a place's value is not defined by its relationship with London.
So, why you would stretch the metaphor by trying to pick arbitrary places for other regions, is hard to understand.
In the modern world, the only time the cliché seems to have any meaning is where there genuinely is a clear / single location that is required to pass for a journey to a place using a popular mode of transport. So, Kyle of Lochalsh, which is a clear gateway to Skye, or Johor Baru, gateway to Singapore or Malaysia (depending on your direction), or where an airport is the only realistic way on or off an island.
