Variety is good.
I've always liked the dramatic shift in vibes from Trial to Trial in ARR. The bosses have different personalities, visual touches to their avoidable attacks, and even Soken basically chooses a different genre for every boss. But, they also played pretty differently too. I don't doubt that even now they try to feel out the vibe of a boss when they create it, it's just that they have so many standards because of how they've designed their jobs and their encounter catalog to look back on showing what players do and don't like/clear that stuff probably gets filed down so that it's like... aseptic.
They've shifted away from fights having mechanics like Titan or A4s* in which attacks are aimed at players, or aimed randomly, opting instead to aim at very "set" trajectories. Compare all ARR Extremes to ShB ones. In ARR, the number of mechanics that hit set positions are like, a couple per boss (Mistral Shriek, Bomb Boulders, Radiant Plume/Dashes, Leviathan's Dashes/Slams, Moogle Delta Attack, Ramuh's point-blank aoe, Icicles). In ShB, even bosses designed to be more freeform (Crown of the Immaculate, Memoria Miseria Ex) have several (God Ray, Rightful Reprobation(Swords that Fan out and return), Beatific Vision, and most of the Starbirths; Reinforced Gunshield (random, but not based on players), Electrified Gunshield (he politely always moves mid before knocking back), and Terminus Ests from clones.
Now that I think about it, it helps inform me why I enjoyed Innocence and Memoria so much more than most of the other extremes. Especially on repeat visits, you need to be more engaged with your other party members and whether or not you're the target of something.
*
(shout out to a4s, as 'not very fun' as that fight can be, it really manages to create 'predicaments' from combining nothing-mechanics. Simple ground aoes are soo much tougher to deal with when you have adds you're trying to keep separated/facing away and tethers you're trying to stand in line with targeted at random players. a3s' Protean Waves/Sluices were like this too later in the fight.)

Originally Posted by
Irenia
...Modern savage fights don't really have that (or maybe they do post door boss, my static aint that good haha).
I think you're right, and that door boss is way more of a brawl. Door bosses generally are, all the way from Exfaust to Hesperos. Ever since StB, Final Savage checkpoint bosses have been categorized by 'here's a ton of bullshit to decipher at once' mechanics, designed to require the group all discussing and reporting debuffs and contributing pieces to solve a puzzle until someone publishes a guide 2 days after the patch.