I would think it’s viable.
I’ve been leveling as affliction, but because of preference and not optimization (because idk what’s optimal for leveling locks). I think affliction is the coolest spec, and so far questing has been a breeze. I’ll send in the voidwalker, apply DoTs, and then Fear and DoT another mob while my voidwalker and DoTs finish off the first mob.
I can usually survive when I accidentally pull 3-4 mobs but definitely have to drink/eat afterwards. When I just focus on one target at a time, I don’t have to stop and drink but like every 10ish mobs (assuming they’re in my level range of plus or minus 2 levels) which is really amazing.
I can solo an elite mob my level if I can keep it constantly feared and without pulling other mobs, but actually struggle to kill mobs that are 4-5 lvls higher than me. My voidwalker can’t hold aggro even if I let him fight for a few seconds before applying DoTs, and once I pull aggro and they resist Fear I’m way too squishy even with voidwalker sacrifice. I guess that’s how it should be though. I’m not complaining.
Also, I’m not usually worried about being ganked (unless by a higher level) which is very nice as I’m on a PvP server during phase 2. There are times when an alliance will start attacking me while I’m currently on a mob, and landing a single Fear (or two if they have the PvP trinket already) on the other player allows me to recover pretty well.
I’m only lvl 35 so I haven’t gotten into the more difficult zones, but I’ve definitely gotten a feel for how incredibly easy it is to level a warlock compared to many classes.
I haven’t played around with destruction spec, but they will still have many of the same tools as an affliction warlock while leveling at least. I’d imagine they probably have to be more concious of soul shards and maybe they’d more consistenty cast spells during a fight instead of DoTs/wanding which might make them stop to drink a little more. But maybe I’m wrong on that, because I really think that they’d still have most of the same tool kit as affliction.
10/10 would recommend leveling a warlock