Why did PLD get such a buff

[Reynhart]

The average DRK OT rotation uses 5 DAs per minute. 4 DASEs, and 1 DACS. So if you add DA effects to things like Plunge and SaE, suddenly DASE becomes almost obsolete if their DA effects are a net gain because they would usurp 2 and 1.5 DAs every minute, respectively. At the end of the day it would also likely nerf or buff DRK's personal DPS, neither of which is necessary.

Like I said, what if the effect of DA on Souleater would only benefit a MT ?
You could have a well designed rotation for MT, and another one for OT, based upon where you use your 5 Dark Arts per minute.

[Syzygian]

Like I said, what if the effect of DA on Souleater would only benefit a MT ?

You'd have to somehow find a way for +140 potency to not benefit an OT.

When you have to start pushing aspects of the job aside to make changes instead of just adding something where there is room for something to be added, you get poor design.

[Reynhart]

You'd have to somehow find a way for +140 potency to not benefit an OT.

I already said such a way :

Increase Soul Eater's basic potency to 350, and make Dark Arts only increase the leech effect to 150%.

You could even increase the leech effect to 200% under Dark Arts, it would help recover after Walking dead, now that tanks will have higher HP pool.