I think RNG is best served for minion drops and cosmetics. Things you can potentially make money off.
Having RNG also to affect your savage or ex trial progression would make me want bash my head on the table.
Eureka exists for those that want a high ilvl item and cannot group up for savage content and time grind is applied accordingly.
Ffxiv makes different content for different players and not all players even will be satisfied with the current options for progression.
For example, i progress in neither savage nor Eureka but i enjoy crafting to help my FC and engage in FC ex trial runs and occasionally PF runs as well as progressing my gathering.
I would hate it if RNG was imposed over systems that arent built for it as getting something will be based on how much free time can you hit that skinner box which is not the game i signed for. If i wanted a loot grind and skinner box I would play that kind of game like Diablo.