I don't underestimate the costs.
literally sit back and last hit with cleavers if you don't have lane advantage with Mundo. You won't run out of HP if you aren't spamming it off CD for no reason. You won't even approach half.
you just last hit until you're 2+ items unless the enemy laner goes full-retard and lets you kill them or goes kamikaze to try to kill you.
Neither have problems with their costs.
costs aren't an issue if you're using the healing portion of W, again, unless you're uselessly spamming stuff off CD. He just sucks at laning in general though.
It would only be useful to
early game, and barely helpful at that. His costs aren't an issue if you're just using them to sustain your shield when you need it.
Believe it or not, but early laning phase is not about spamming your spells off CD. Its about managing your resources so you can afford a good buy on your first back, rather than giving up the lane or being forced to back.