The pressure curve is related to burn rate, and thus burn time. If a particular mass of powder burns completely well before the bullet reaches the muzzle, you’ll have a lower muzzle pressure. On the other hand, if it burns completely just before the bullet exits the muzzle, you’ll have higher muzzle pressure. And of course if it doesn’t completely burn until after the bullet exits, you’ll have a completely different effect.
MV is related to the pressure curve, but also a whole lot of other factors, so it’s really only mentally useful to think about when comparing different loads of the same powder.
GRT should tell you not only whether or not the powder is burned 100%, but (on one of the curves) where in the process burnout occurs. When tweaking a load for a particular velocity range, that information might help you zero in on your load.