No, not really. It's unforgiving compared to modern MMOs, for sure, but it's not as punishing as some older ones. I kind of like it as a medium-core MMO.
I'm talking mainly in terms of death penalty. Like, in Everquest when you die you lose experience and drop all of your items on your body (on the Rallos Zek server if you died in PVP, the player who killed you could loot an item off you). You then have to either run back naked to where you died, which might involve getting a Rogue friend to sneak in and drag your corpse somewhere safe, and/or get a Cleric to resurrect you (which is vastly preferable since their rezzes would restore some of the experience loss, up to 98% if you could get a high level rez!).
Or going back to like Nexus TK, when you died you'd lose a hefty chunk of experience and all of your Break On Death items, uh, break. And then they're just gone and you have to go buy them, farm them, or win them again.
All that said I think WoW hits a good sweet spot where you're not an unstoppable god blowing through the content, but also dying isn't such a gut-punch. Don't get me wrong, being legitimately afraid to die makes dungeon diving actually seem dangerous and adds to the immersion, but I also don't mind losing them for convenience's sake.
That said I'm not sure why WoW got the reputation of being the casual MMO, considering a much more casual MMO also had a big launch a few months prior: City of Heroes. I just played that on a private server for a bit and, XP debt aside, it feels much more approachable and casual to someone who's completely unfamiliar with MMOs or RPGs. I guess just because WoW ended up being that much more popular.