I am not arguing why Modern Assassin Job should exist with my comment. I am Arguing about that Astrologian and Gunbreaker did exist in past FF games even if they did not look like they do in FF14 today. Not to be rude nor offend you but the only one who is currently thinking I am trying to justify introducing Modern Assassin job using Astrologian and Gunbreaker is you.
As I said our opinion of what can and cannot be considered a new Job in the FF seres varies because, in my opinion, you based what is a new job in FF series by their skill and how they are designed currently rather than how they are designed in the past before FF?? Game and the influence these past versions had on current versions of the Job today.
I based the idea of a new job in FF series based on their history no matter how small they started out in FF series because their origins is what leads to their identity in current and future FF games as these game expand and add more to these jobs.
As I said before, Astrologian did exists before FF14 but it was basically in its infancy stage being the only thing that existed was the name and character identity it was linked to being Orran from FFtactics. It is from there we see the origins of Astrologian job in FF game series as this is where Astrologian Job earned the first recongnition in the FF series then it finally got expanded on by introducing the new skills in FF14 which some skills became inflenced by Orran's lore in past FF games being the Tarot cards mechanic. Yes, Orran himself never had these skills that FF14 has for the job and only had Celestial Stasis but he is the first character to introduce the Astrologian Job by name and introduce the signature skill Celestial Stasis into the FF series. As FF seires continue the Astrologian Job can be expanded even more in the future in other FF games adding things into the Job identity that not even FF14 added into it.
Same with Gunbreaker Job being originally Squall Job in FF8. It did not have the name Gunbreaker yet back then but it was unique to Squall/Seifer when FF8 was introduced and was commonly referred as Squall job or Gunblade Job until FF14 gave it a name to go by being Gunbreaker. The identity of Gunbreaker Job get expanded even more into Lightning as she introduced the more Gun function version of Gunblades with her gameplay and take on the Gunblade Job. We then see its return in FF14 with the lore of being the original version of Gunblades and Garlean version being a separate copy in the opinions of the NPCs. We can see both influence of Squall/Seifer/Lightning when the skills were designed such as Squall/Seifer combat melee skills with the Gunblade and having Lightning's offensive gun function replaced to fire the defensive Light Barrier Ammos. We can expect future FF games to expand on this more that not even FF14 current may not be able to thus adding more History to the what was once called the "Squall Job" and potential skills the job can do as FF series expands on it in both future expansions of FF14 (still got a new set of Expansions of storyline in 7.0 and beyond after Season 1 ends in 6.0 to 6.3) and future FF games that introduce new characters that uses the Gunblade.
Dark Knight, as another example, did not begin as we know it with Cecil but instead did start out its life in infancy with Leon. Leon gave the Dark Knight Job its very existance into the FF game being the first character to have the Dark Knight Job in FF2 and then the dark knight obtain its job skill identity in FF4 with Cecil take on the Dark Knight and introducing the iconic skill Darkness.
The past history of the Jobs are important no matter how small they are in the past because they are what builds these jobs into what they are today and influence their design. You can discard any past iterations of these jobs all you want simply because they do not have the skill kits they have today but you cannot discard how heavily influenced they are by these past iterations even if they started out with only a name, or without a name in certain cases, a character it was once exclusive to, and a few skills.
I say the Job's history is important no matter how small it is. Certain jobs did start out as simply altered or slightly better versions of X or Y job but will later become more unique through several iterations in other FF games. It usually begins with a Job name and/or character they associate with then expands into what we know the Job as today through the additions and alterations of the Job in multiple FF games by the additions of new skills unique to the job and through their lore in those FF games that originally never existed in past FF games.
Leon from FF2, for example, is the one who created the Dark knight name and iconic appearance with his armor in his arts for the FF series but due to how he was in FF2 with his skill sets certain amount of people do not event recognize him as the OG Dark Knight and will default to Cecil because Cecil established the iconic Dark Knight identity with Darkness. When hearing the name Leon, they often default to Squall Leonhart instead due to his name being Leonhart as well and due to how Squall established the Gunblade Job identity into FF series.
Everything has a origin no matter how small it is and through that origin they build on top of it by adding lore, skills, and appearance additions we know them as today and in future iterations though multiple FF games.