It honestly just felt like people liked Heavensward because it wasn't as strict ie. you could meld stats you weren't supposed (like Mind on a caster DPS), using other job's accessories, meld elemental materia, etc. There were lots of problems with Heavensward, and some people find overcoming design problems fun ie. trying to make Paladin better at DPS than it was. Perhaps because of the feeling of "wonder and possiblity" it creates when developers give you freedom to break their intended rules.

And some people also liked the annoying and clunky design of jobs with a lot of pointless abilities that just made them annoying to play, and perceived it as "job complexity" in a positive way.

But all those things were changed, removed and made strict for a reason. They were usually pointless and not a good thing, and only served to confuse new players.

And how about Parry, physical mitigation against magic bosses and having to stack Accuracy just so you can qualify to raid?