Well "nerfing" them still leaves them being one of the best choices in the book....and you can still cast spells on them.
And i don't need to cast spells to have good hiting unit anywhere else.
If you need spells to make some unit great, then that unit isn't great, right?
One bad dice roll, and your ENTIRE UNIT of DGK is wasted, broken, cought and destroyed.
And that's just one bad dice roll of chickens, riders are usless there.(Compared to proper MC units, Mournfang, SkullCrushers)
So, we have unit that is completly usless if it gets bad luck on dice, expencive, and pale in comparison with EVERY OTHER MC unit(yeah, even Tomb Kings have better MC unit).
For points invested in 4 dkg with command, and possibly some banner, you can field 12,13 KIC that will get reroll, hit more and kill more.
4dgk are 12 chicken attacks, and 5 usless attacks.
12(s5)without and 5 with reroll
On the other hand, we have 13 rerolled attacks.
I would always go for 13 rerolled attacks more than possibility that maybe i will hit. And good chance that i will completly fail and waste nice amount of points that could be invested in 2 cannons that never failed me. Failed to hit, yeah, but were a threath. Unlike DGK.