They have a very easy out here. The Musketeer Guild stuff still exists in the game. Hence I would be surprised if they didn't use it. Thus they have the opportunity here to add it as a starting class/job. Now if you already had a character at level 30+, then by all means switch directly to the Gunbreaker or Machinist. This is why new jobs introduced start at 30, so they don't have to write a level 1-30 story that to be fair most of the level 1-30 content for the all of the jobs plays the same, because they have to be in the mainland Eorzea ,which if a new job was introduced by an expansion, would not make sense to do. They could do it here though.
Now how they added Red Mage and Samurai was really backwards. So both of these jobs start at level 50 in the Eorzea 2.0 areas, so if you don't have an expansion pack or haven't finished 2.0, they will be stuck at level 50. But you can use their entire skillset upon acquisition. These both should have had a level 1-50 story to them, but clearly they didn't feel it was important for the players to lean the skills in easier content first.
So here's my opinion, I'd rather see it start at level 1 and be a starting option, but it can start at level 30 if it's meant to be a "learned" job like Machinist. If it's meant to be a freebie to the base content like RDM/SAM, then by all means start it at the previous content's level cap. To me I would feel cheated though. I also feel that other players get a very negative impression of a newly introduced job when the players have had no time to learn it, which is what RDM and SAM was in high end content.
