I’m fine with crit melee (though I’m sure many wouldn’t like it). The box would not to be very small. As it is you can hit 4-5 people with a melee in a grav. So the possible hitbox for crit would have to be dead centre of melee hitbox and close by. Without that change you’d crit even if you hit them in the chest.
However it’s worth remembering that this will reward certain heroes disproportionally. Tracer or Genji for example get way way more value out of this than other heroes because they melee more often. As an example I can’t one clip with Tracer often because I’m bad (and it’s hard). I can’t even 170 that often in one clip which means I can’t blink melee recall to finish most of the time. But if all I have to do is land 140dmg before blink melee it becomes much easier. Genji is all about melee combos. Hog would get guaranteed kills on most 200hp heroes now… which I wouldn’t be opposed to. Comparatively a hero like Ashe or… well probably 2/3 of the cast rarely use melee. When you make a change like this you have to evaluate how it affects the potential of different heroes. I don’t think it’s a change we necessarily need and it’s a power creep.
15/30 melee sounds kinds useless. Again it would disproportionately nerf heroes that rely on melee and I don’t think those heroes (Tracer Genji) need a higher skill floor.
Idk why the obsession with crit melee. But I can tell you it’d be better received as an actual critbox not a random crit. RNG elements just suck.