I always play melee because their armor is the tankiest and I'm a cheapskate who's allergic to the concept of expending ammo. Can't abide the squishiness of the other armor sets. I only need potions for Moon Lord anyway, and dying to him is never a question of running out of buffs, it's just bad luck with the True Eyes.
(Plus, you've got to love Solar Flare armor when you're building. All the enemies that run into you explode and die and you never have to pay attention to them.)
But yeah, if you're fighting WOF and you're relying on obsidian skin potions, you're doing it wrong. It's not that immunity to lava isn't useful during the battle, but it's stupid to fight it without setting up a bridge. The Wall of Flesh speeds up as the fight progresses - if you rely on the natural terrain, you're likely to slam into a helltower that stretches from floor to ceiling sooner or later, and you'll get sucked into the mouth because you don't have the time to mine your way through.