true, Poland lost out in terms of sq.km. but it wasn't / isn't the disaster the Hungarians still have to live with nowadays.
The land that Poland gained is the west is less fertile than the land that they lost in the Ukraine. The soil in the Ukraine is more productive because it is less sandy in substance.
As for the east of Poland as a whole and its underdeveloped state in comparison to the west, that is in large measure explained by that the fact that the eastern front in WWI just happened to be in today's eastern Poland and a bit of today's western Ukraine and Belarus. They also took most of the brunt in WWII.
Oh and lets not forget the Bolsheviks after the 1st war.
isn't the disaster the Hungarians still have to live with nowadays.
Actually the Hungarians don't have it that bad, they have far more land to go around than the Poles, in therms of population:
Poland: Density 120/km2 (83rd)
Hungary: Density 107.2/km2 (94th)
Plus Hungary is far more fertile than Poland.