Can I go to Ishgard right after purchasing Heavensward? Yoshida says "No".

[Aduu Avagnar]

The only things I need to do at this point is to level thalmage 3 more levels and archer 4, so I can have DRK to go with me PLD and WAR. (Im betting DRK will require lv50 PLD and a lv30 BLM.)

 

Other then that I have to finish leveling my FCs crafting classes.

I doubt it will require THM in the same way that NIN doesnt require THM. Primarily because cast times on a melee class tends not to work , and those are what the THM brings as Cross Class abilities

 

But to address the overall thread, yes it is odd that they are restricting access to Ishgard in a general MMO perspective. However, I don't think they expected people to go the length of ARR without touching the MSQ at all, in hopes to do it on an expansion class. And it also makes sense from a story perspective, having played the MSQ.