Many of the more streamlined MMOGs, which exist only to capture users for commercial exploitation, continue to employ concepts such as vendors, repairs, crafting, and the like mostly as a way to add some variety to their combat–focused experience. Also because that gives their users one more thing to do in their grasp.
Most of them have since pandered to the impatiences of their users and consolidated many of such needs in cities which place the provisions together at short distances.
Sure, there is some novelty to having a certain trainer or immobile re-agent — workcenter, what–have–you — in a distant dungeon or village, but eventually, if the MMOG is designed for dungeon-running or raid-battles, that trainer is either useful or is slowly obsolved and falls into disuse. If it is useful, then it is eventually moved to one of those major cities.
Of course, stuff like that happens for the sake of convenience in our world, too. It may be nice to browse a market, looking for exotic wares, but once we've settled on things that we like, we tend to prefer the more convenient source for our supplies.
That's what should be simulated: If you want to consolidate things into one place, then you need to consider the logistics from the perspective of a person in–universe.
What does it take for them to decide that it is profitable or feasible? How long would it take for them to establish a consolidated workcenter?
There are some MMORPGs which make things like that a part of the gameplay.
As for storage: I've never like banking or storage via NPC. Where are our caravans? Our sapient pearwood chests? Our portable holes? (Oh, bother.)
Even rentable carts and wheelbarrows and lorries would be better than stationing an NPC who magically retrieves and stashes your materials.
Final thought: remember that the purpose of the Yliakum world is to enjoy it — whether for the sake of a story or for the simple beauty of the environments. If everything is in Hydlaa, then be sure that the other parts of the world are not neglected or diminished — unless that is part of the story.