If you're only doing the 1.4 AP + 450 base damage you're still stuck in the burst combo mindset for Malzahar, which, yes, has become suboptimal for him. Maximizing time on Malefic visions by using its refreshes you can achieve almost 25% max health + 2.8 AP + 890 base damage, plus voidling damage which is dependent on voidling numbers so I can't easily calculate it in. This is with one full rotation of spell, including your ultimate. This is also not counting the additional damage a surviving enemy would take trying to leave the pool, which lasts twice as long as the grasp, or the increased pool damage to other champions standing in it.
I'm not sure why you think he's not a hyper pusher now, his voidling swarm pushes incredibly quickly since he has so many more voidlings than he used to.
The passive exists as it does now because it was trivial to CC Malz out of his ultimate in the past, thus reducing his damage quite significantly since Nether grasp was a large chunk of his damage in his full combo. Yes, the passive is what allows him to work, but the lack of any kind of CC immunity was what made Malz relatively weak against any team who coordinated properly and CC'd him the moment he started to ult before his rework. Even without the CC immunity, his damage output would still average about the same or higher than previously (accounting for voidlings), it's just more spread out than it was in the past.