I don’t think it’s that simple there.
Class choice is a much more substantial and core gameplay choice, where as choosing covenant is effectively just choosing 2 active abilities and some additional layer of talents via Soulbind. On top of that choosing a class main is serious commitment, where as covenant you will be able to drop and change, even with this cost they mention.
If I have a decked max level main I play for years because of class fantasy or simply because I like its gameplay, I won’t go ahead and reroll it a whim, because it’s a massive grinding headache and a huge change and if in patch X warlocks are shit, then many will tough it out because rerolling is a big investement. Covenants? IMO the costs are not quite that steep to prevent minmaxing, people will most certainly go for optimal choices.
I only hope there will be more than 1 optimal choice there, although I am sort of skeptical seeing some Kyrian abilities given - for some classes/specs these abilities are like OOooOoooOoOOOOOoo, but some other abilities look like utter shit. For example Kyrian ability for DK is complete dogshit for any DPS DK, while Mage one looks insane.