Working back...
House Orien, that has been around for hundreds of years, offers expensive magical trains, but doesn't have a teleportation circle network between the major Metropolis and Cities...
True. In 3.5, the concept was exactly as others have stated; there may very well have never been a 17th level wizard in the history of House Orien. Even Erandis Vol isn't that high as initially presented (I've always seen her as a villain whose capabilites should change over the course of a campaign). Eberron is wide magic but not high magic. Yes, this may seem strange with some other CLs suggested, but as we've said the point there is that the houses use focus items to get around that. One thing I'll note is that this is why House Cannith is so powerful; other houses need their amplified Making to create their most vital tools. The lightning rail, wheel of wind and water, Kundarak vault network, and other things are the result of multiple houses working together, amplifying their marks with focus items; this is one of the main points of the Twelve, helping the houses work together to prosper in ways they couldn't alone. The fact that a 15th level PC could make an airship on his own makes him AMAZING, because normally it is going to take a whole crew of specialists.
In 3.5, the Inspired actually DO have a teleportation circle network, described in
Secrets of Sarlona. It's something that distinguishes their society from Khorvaire.
4E messes this up by dramatically lowering the level on Linked Portal, and this is why you see the portal network mentioned in The Fading Dream. In my campaign, Linked Portal is currently unique to the Mark of Passage; no one has created a ritual to let any ritual caster use it - this is why it's a big deal for Drix to "hack into" the network.
Besides that, PC spellcasters could become rapidly rich attaining a level sufficient to cast Teleport, and offering their service.
Sure, if that's their idea of a good time. Honestly, I don't think Orien would care about a single wizard who occasionally takes gold to do a teleport job; teleports are a small part of their income, with more being based on the caravans, lightning rail, and other large-scale industries. Now, if the PCs started a network of teleportation circles or something like that, it is a direct challenge that threatens the house, and I'd expect them to respond. But perhaps the players can work with the house. Perhaps the players can overthrow the house. That's adventure. In 4E, this would be a PC created a linked portal ritual anyone could use (again, solely in my campaign where it's limited).
Regarding the Knights Phantom, as others have said, you don't have to have levels in the PRC to have the title. This is also a case of inconsistencies between books; some designers overlooked the concept of Eberron being a lower-level setting. However, with that said, there are 5th level wizards in the world; the point is that a 5th level wizard is an impressive individual whose skill should be recognized - IE, he should be something like a Knight Phantom. Take a look at the
Dragonshard on this subject.