I wouldn't discount the added roadblock for RMT, but it may also be something they did for consistency. The SMN job quest doesn't make much sense if you haven't beaten Ifrit:

A request has come to our guild from the Sons of Saint Coinach─an organization of some of the finest minds in Eorzea─and they have asked for you by name.
It appears that the research the Sons are currently conducting would benefit from the assistance of an arcanist─specifically one who has had the tempering experience of defeating the primal Ifrit.
Though I must admit to some curiosity as to how these scholars knew the extent of your heroic exploits, I suppose the source of their knowledge is of little relevance...
And they might just want it to be fair for all jobs to have to get to the same point.

Sylph Management is also after you join a GC, so it's the first quest where there's one story line for everyone, with no variations on starting city/GC affiliation. Not sure if that factors into the other job quests at all.