This is a good point. The 6th edition mechanic for Horrors is just generally outdated for 7th Psyker rules, to the player's detriment....hey look I spent all the points on getting them to be 3 warp charges a turn. What's that, you only roll based on mastery? So just once? Hooray.
If only they had updated the CSM and CD books instead of starting in with all the Daemonkin stuff :-( we'll see if there's a Tzeentch book that improves things or not.
I didn't said it made the army "unplayable," I said it was crippling to the point of where I probably won't bother bringing it to a tournament even though under RAW it's my favorite and best-performing army. I've played with CD summoning psykers at a bunch of tournaments ranging from the first big one of 7th (WGC last year) to a big tournament two weeks ago, across three different cities under various metas with all the new stuff coming out every month. So I think I have more than even experience and practice to judge the extent of how much this impacts CD Psykers and competitiveness.