FFXIV is all about incremental increases.

Mostly due to the way that everything scales multiplicatively, rather than additively.

Like, you complain about Astrologian card buffs for 8% damage increase? Well, you add in a jobs self buffed 10% damage increase, something like Trick Attack futher buffing damage by 10%, a Summoner popping Devotion for another 5% damage increase and even the Astrologian popping Divination for a further 6% damage increase. and now you have someone who's dealing 145% their normal damage. So if you'd hit for 1000 damage, now you hit for 1450 damage. Which will then get amplified by Direct Hit and Critical Strike modifiers (With Crit modifier scaling based on how much Crit stat you have)

If buffs were made to feel "Worthwhile" stand alone in the current system... So the same scenario was 20% damage increase cards, 20% self buff, 20% Trick Attack, 20% Devotion and 20% Divination... Someone would, under all these buffs, be dealing a whopping 248% damage, turning that 1000 damage into 2480 damage, which would be insane and thus a balancing nightmare.

For such a system of "Meaningful buffs" to work, it has to be one of mutual exclusion. So that for example, a card providing a 20% damage buff wouldn't stack with say, Divination's buff or Devotion's buff or Trick Attack's buff or a self buff like Raging Strikes. Which shifts the dynamic of buff application from one of stacking buff effects together to spacing out temporary buffs to attain as close to 100% uptime as possible.

Which is a plausible alteration to make. But not one I think the developers would like to utilize (Mostly because it can create anti-synergy in compositions where you wouldn't want to bring class X along with class Y because they both provide the same buff that doesn't stack)