Actually, the Prime and spell caster cost reduction in SE opens a new way of playing for us, making our HQ sniping even more deadly. Imagine you get ever blazing comet + warp lightning + prime comets rod combo. It is average 8 MW output before someone can even move, which is scary for a lot armies. Though it cost a lot (300+90+100) but at least it can be handled as alley (100 for comet is not counted as alley points so 390 from SE). Also, if our points reduction come true, we all get around 120pts freed now.
BTW, I have played with some really experienced players with KO. Some matches are just completely hopeless. My impression is KO got very bad matches against most 'out of board deep strike + ranged' army. Typically Seraphon, SE with raptor, CoS living wood with iron drake. Also teleport + ranged army can ****** you up if they get fewer drops, like Tz and another lower drops KO.
Besides that, several bad match includes:
ID, their Ishlaen Guard makes our shooting completely useless
Orcs with revive boyz, just not enough fire power to stop them screen
Some niche list from Skaven and Fyre Slayer with heavy 'out of board deep strike + ranged'
Some other niche list focusing on -1 hit from range, like certain Ogre, DoK, SE with start dragon and Nurgle.
Generally speaking, I think KO plays a moderate role in the meta. It is efficient against some very popular enemy like Bonereaper, Realmlord, also extremely hopeless against some others. The reason why KO seems quite strong is, when a player knows very little about how KO works, they will lose so quickly against our gun line.