Say what now? MM is superior (in terms of damage) whenever you are targeting just one target (and often when targeting something with a good save, even if multiple targets).
MM is 3d4+3 damage to one target, so 10.5 of guaranteed damage (auto-hit, no save).
Burning Hands is 3d6 damage to one target, or half on a successful save, so 10.5 or 5 damage (strictly worse to one target).
Thunderwave is 2d8 to one target, or half on a successful save, so 9 or 4 damage (strictly worse to one target).
Now the other two spread to additional targets easier, but they also hit your allies in that same range (baring a special ability). So that's quite situational. MM can also hit multiple targets with no risk to allies, though the damage goes down.
MM is a very high utility spell. Our caster has made a lot of good use out of it, up through 5th level. Auto-hit is pretty damn handy.