The weather and traffic models will be global since they are not being sampled in real-time. You don’t get different live weather for a particular location depending on what servers you’re on (well, not on purpose anyway!). I had always assumed that ‘servers’ meant the geographical allocation of Azure resources replicated around the world, and that the primary reason for switching servers is to achieve lowest latency and best performance based on where you are physically located. Latency from Europe to SE Asia, for example, is very high which is why MP performance for the Community Fly-Ins can be patchy for me.
Having multiplayer be local to regions has always seemed odd to me, but I assume that it’s simply impractical to replicate enough data in real time to maintain a single global multiplayer pool. Each individual player would only see a local ‘bubble’ of nearby players in any case. But it seems odd that someone connected to North Europe but flying in Australia can’t see players connected to South East Asia and also flying in Australia, and I would have thought that would be a desirable thing if practical.