FYI the patching issue is not consistent, myself and 3 friends have never had issues patching, however Australians do run into this issue far more than other regions, I know multiple people who have been completely unable to patch, one has also then still been unable to patch even after getting a brand new PC and moving to the other side of the country with a completely new network setup, VPN is the only thing that allows them to patch, and it doesn't seem to matter whether you're using Steam or not.
The restrictions imposed by high ping are really not part and parcel at all, when I played WoW on US servers, there was basically no difference in what I could physically do, the UI would do some funky things sometimes but it never prevented me from pushing a button that a low-ping player could push at the same time.
In FFXIV there are mandatory changes you have to make to some rotations depending on class when you're on high ping, and it locks you out of the freedom to double weave, a lot of classes have a guaranteed DPS drop on high ping, tanks can't emergency double defensive, etc.
In easy content it doesn't matter at all, it's easy, the performance drop only matters when that performance drop costs you a static slot, or requires you to spend an extra week getting gear to down the DPS check dummies, or gets you killed in pvp by someone on 1% health that a double-weave could have killed.
However, even keeping in mind that this mostly rears its ugly head in high-end content, it has flow-on effects, how could they consider decreasing the GCD if it would probably increase the gap between high and low ping DPS? How could they start changing rotations to make double-weaving more standard if a chunk of their playerbase isn't allowed to double weave? What about NIN? I heard some people were a bit annoyed about the Mudra changes, but would those changes have been necessary if there wasn't a big group of NINs who were neutered by high ping?
The high-ping issues are most likely a legacy problem, I don't think I need to explain just how little Square would have been thinking about responsiveness at 200+ ping when they were first making XIV 1.0, but the issues in this game are very specific to this game, they aren't just how ping works, they're caused specifically by a lack of adaptability to high ping.