I think he was talking about having to re-gear for a different build as I've seen that point come up other times following nerfs. It could be meant something else by the comment. And I don't think people will have to switch from warlock, but they feel it's necessary due to the power loss. My opinion is that warlock will still be the easiest casting class for reapers because of the free dps, but wizard in my opinion will be stronger in the hands of some players.
I include level 21-30 because for the people wanting rxp in addition to racial lifes it's a no-brainer to run epic content for rxp even if you already maxed out your epic past lifes.
There are many variations of warlock builds and all are easy to play. To the extent charming, necromancy, enchantment and illusion is added the builds benefit from past lifes/gear much more than a simple blasting/Tentacles build and that is true whether they use cone/wave or burst/blast. ES is the most popular because of the defenses and self healing, but SE/TS has always been popular as more of a glass cannon blasting build maxing crit chance and damage.
Casting other DC spells besides eld blast related shapes and slas isn't really all that hard to play, it just benefits alot more from investment compared to a straight up blasting build.