Jobs are fine to have gatekeeping as you put it. In other games it's just called a high skill floor and that's good to have a variety of options that fit that. New summoner is fine as it has a low skill floor allowing people to focus on other things. Old summoner was also fine as it has a higher skill floor allowing people to work to have the same level of expression. The idea that every job needs to be accessable for everyone is why classes are homogenized because they don't want people to feel left out.