Why does Leblanc have 335 movement speed?

This isn't a QQ thread about Leblanc nor is it a cry for Kassadin buffs. The two champions are quite similar to each other and have been compared to each other many times in the past and I'm just using him as a comparison. It just seems like she should be paying for that insane mobility.

So I'm asking: why does one of the most freely-mobile mages not have some very low normal movespeed? She has so much mobility that works as an escape, a re-positioning tool, a juke, waveclear, and high burst damage. Her dashes are still super quick and do not require a target and can go anywhere up to 600 range and deal damage at up to 850 range at will (she has 1550 maximum range with her chains without using her ult). Why is it that Leblanc gets near unlimited long range dashes with some blinks when kassadin gets his ranges nerfed and increasing costs for using his movement ability? Leblanc gets CDR in her normal build too which makes her even more mobile. Kassadin doesn't get that luxury either because he needs mana, not mana regen. I know Kassadin has 340 movespeed but he is melee and deserves to have higher movespeed than Leblanc because of that. Should this extremely bursty and incredibly mobile assassin not be made more punishable for making a mistake?

Leblanc seems to get to have her cake and eat it too.