If the new assassins are even more mobile than before, then why do they get a spellshield?
Ruot has said over and over again that asaasins should succeed through creative use of their mobility. If I am a skillshot mage, who already has enough troubles with champions like Zed, Talon, and Kha'Zix, then I should at least have the satisfaction of being able to hit my spells when I outplay THEM.
Mages have access to Zhonyas because they are immobile and easily jumped on. Giving assassins more defensive tools, when they are already super mobile, is a mistake.