Malzahar balance issues - Specifically about his spellshield

I recently was Playing as Ashe ADC, and realized as Ashe, Malzahar's spell shield renders him 100% immune to ashe. Ashe's passive has critical strikes apply slows, and so Malzahar is even immune to Ashe's auto attacks. Malzahar's immunitys are so widespread, and his damage so potent at this point, he feels like a tank, not a mage. The thread I linked has him building Attack damage in which he is soloing rift herald at level 5, dragon at level 3, etc. He's usually banned, but also a common pick, and I feel he needs a strong nerf, when he's immune to one of the most common adcs, to where he can't be damaged, you need to re-think his kit.