You’re eating the wrong kind of mangoes, or eating them wrong! This 3lb mango from my brother’s tree has a very thin seed, so it was very easy to slice off two thick slabs to cut in squares.
I did it while camping instead of in a proper kitchen, though, so my fingers were too sticky to take photos until after we cleaned up, and by then all the mango was devoured. The seed is shown here, which I didn’t weigh, but the ratio was definitely very flesh-heavy:
The elongated mango types usually have very thin seeds, so you can cut off slabs to cube easily, without leaving behind very much to be sucked off the seed (my favorite part, but definitely messy). Rounder types often have thicker seeds too, so those can be a little more tricky to cut up.