Do you code for a living? Do you know how badly the base code is for this game, their running off of shoots of 1.0 which is why at the end of the day "we don't get to have nice things". If you're asking for older classes/jobs... which you did in your OP... than they have to readjust the coding for that because gladiator equals paladin and for anything else to get added to it you have to work it in to that base class (or just abolish the thing to begin with.. but again major rework). Also, the whole point of this streamline was to adjust it so they don't have to retweak everything for the next expansion (Shadowbringers was the first major over haul of the whole system, the previous ones just added and tweaked a few things.. this was definitely a overhaul and other than healing, if their even considering that, I don't think they intend to overhaul the rest of the system).
Like I said previously though, trying to give access to the jobs outside of Ishgard don't make sense not just for lore (which is already gutted enough at this point) but because at the end of the day you still have to go back and rework it so that it can happen... it's not just put character here to let you do things. You are right it may seem weird that you can be the other jobs, although other than samurai and red mage again if you're unlocking the other jobs and haven't gotten to Ishgard you're playing the gave very weirdly.
I've played several games like this and yes they always try to rework things to make things easier to catch up, they've done that since the beginning of Heavensward.... what were talking about is completely different. They went back and slashed out quests that don't matter (and their not returning them into side quests to go back and do for later) and it's because this was filler stuff that didn't need to be done, in order to stream line.... and while that may seem like an easy task it really isn't and this rework is the major reason why were getting so little content this expansion.... they've mentioned this.
Leveling isn't that hard in this game, it can be tedious but than again most aspects of MMO's get that way. It's the nature of the beast.