Make BC's E scale with Mana instead of AD

Right now his E does 2x of his AD as physical damage. Plus, his W gives him a decent amount of attackspeed. But I just don't see the point behind it. I mean, when do you ever build AD as a support, especially now that the old Zeke's is gone? What most tank supports build instead are tank items that often also give Mana, especially Blitzcrank with his passive. Righteous Glory, Frozen Heart, Frozen Fist and Zeke's. Making his E scale with Mana would just be the logical conclusion.

Since his E does about no damage it also means that a lot of damage has to be packed in his ult and his Q right now. They both are spells with a 100% AP Ratio and 300-500 base damage at max rank. This is a big problem since he has no DPS at all and only burst damage, packed into his Q and his ultimate, his Q being unreliable since it is a skillshot and both spells having a really high cooldown. This means when he has one of either spells or both of them on Cooldown, the vale of his kit just plummets. Removing a bit of damage from his Q and Ult and packing it into his E would make his damage more reliable and not so reliant on spells that have 16-30 second Cooldowns so that he is even worth a damn while they are not available.

I thought about something like that :

E: Power Fist: Passive: Blitzcrank's basic attacks deal 0/15/30/45/60 (+5% of his maximum Mana) bonus magic damage Active: Blitzcrank's next basic attack deals another 0/15/30/45/60 (+5% of his maximum Mana)(+40% of his AP) bonus magic damage and knocks its target up for 1 second Cost: 25 Mana Cooldown: 9/8/7/6/5 seconds

rather than what it is right now:

E: Power Fist: Active: Blitzcrank's next basic attack deals 200% of his AD as physical damage and knocks its target up for 1 second Cost: 25 Mana Cooldown: 9/8/7/6/5 seconds

Since Blitzcrank is already kind of working right now, at least in SoloQ because his Q does not get countered as much as in competitive play. This means if that change would actually go live some power would probably have to be stripped from his Q and his Ult. I already pointed that out above. Reducing a bit of base damage and AP ratios from his Q and Ult would seem like a good way to balance it out.

Would love to see some thoughts and criticizm on that.