Both of you are simply describing the limitations of the PS4 itself not whether it impacts XIV's development. Unlike the PS3 where the devs literally couldn't add UI improvements without breaking the console, they haven't run into any noteworthy problems evident by the graphic update going through without a hitch, albeit in a very reduced state for the PS4.
Put simply, it running at 30 FPS and struggling to load 300+ hunt trains doesn't matter so long as it isn't impact the devs ability to add new features.
Obviously, only SE has those exact numbers, but it's hardly a reach to suggest a not insignificant amount of XIV players haven't upgraded when 50% of the entire Playstation playerbase hasn't. If that number remains high, there's simply no chance they drop support and risk losing them. Especially not when the overall XIV playerbase has been in a pretty steady decline since DT launched.
Not according to these articles which place the PS4 userbase at 59M
https://gamerant.com/ps5-sales-numbers-compared-ps4/
https://tech4gamers.com/playstation-users-half-ps4/
Even in your article, it still cites 50% of the Playstation install base is actively playing the PS4.