The devs were unhappy because they have trouble balancing samurai's damage profile.
Most of Samurai's damage comes from their big hits: Midare, Kaeshi Midare, Ogi Namikiri etc. As such crit variance will affect the performance rather heavily.
This in turn makes the tuning in ultimate rather tricky. Because unlike a savage fight that is mostly full uptime, an ultimate fight has short bursts of phases where you can do damage, and various other transitions and forced downtimes where they run you dizzy with mechanic vomits.
If 6.08 samurai critted a majority of their big attacks within the available damage window, that could make the DPS check trivial. Conversely, a samurai with terrible luck would not be able to reliably contribute to the DPS check.
This is in theory how I interpret the devs' intentions based on current ultimate design and their words from the patch note reading. But I still don't agree with their decision to remove kaiten either way because there are ways to smooth out samurai's damage profile without removing kaiten.
In practice however, the damage resource structure of a job leads to more balancing mishaps than crit variance.
Take NIN for example, most of their damage comes from things on a CD (ninjutsu charges, trick, kassatsu, dwad etc). Losing GCDs only means a loss of ninki generation which is only a small part of damage make up. (take the top p4s p2 nin log for example, bhava only accounted for 9.45% of their total damage, the bunshin attacks adds up to less than 5%).
In a similar boat, a BLM can simply umbral soul away and continue charging polyglot stacks during downtimes.
Meanwhile, GNBs are on suicide watch with the cartridge alignment, MCH and RPR needs to hit their GCD to build up resources for their burst phase (I can hear MCH internally screaming over drill drifts), and every 8 GCD lost on SAM is 1 less midare and 1/3 less shoha.
So in the end, I don't even know. The new ultimate is without a doubt a spectacularly designed fight, but the individual job balancing is... confusing at best.