This supposed "rework" of Raijin only serves to completely screw him over. People complain about Raijin only because they don't know how to use him. Raijin is my 2nd fave mage after Anubis and I almost constantly wreck with him having top kills/damage, even when I lose. He doesn't need to be reworked other than dropping the cooldown on Raiju, helping his mana hunger and fixing the occasional glitch with his ult where he sits there and can't fire his final shot.
-Mana Costs: Dropping these for his abilities is a good idea. Even with Chronos Pendent, he's still mana hungry until you get Tahuti and even then it can still pose an issue.
-Percussive Storm: Love everything about the changes to this except for the power scaling decrease. That's BS and isn't the least bit necessary. Unless they're basically 1-hit, you won't even use this on them except to trigger Raiju. And considering how hard it is to hit 1 shot let alone all 3 right now, the fix on this is well deserved and appreciated.
-Raiju: Changing Raiju to a DoT removes half of Raijin's burst right there. It doesn't need a slow either. Built right, his 2/1 combo will take out about 60% of any squishy god's health. Not only that but dropping the power scaling, even if only 5%, adds insult to injury. You've taken the strongest part of his kit and basically thrown it out the window.
-Passive: His current passive is fine and serves to add to his burst. All you need to do is put Chronos Pendent on him and he's good with CDR. The only ability that's an issue with cooldown, again, is Raiju.
-Ultimate: Cutting the damage from his ult's 2nd and 3rd beats? Why? They already do half his damage anyway. You need to use the 1st beat to do full damage. And decreasing the speed of his shots? WTF? They're already super easy to dodge! Unless you use the taunt first, you're not even likely to hit with the 1st beat. Slowing them down serves only to make his ult worthless.
-Thunder Crash: I don't know what you're talking about with him not being targetable during this. I've been killed many times before I could finish the teleport.
TL;DR: Drop the mana costs of his abilities, lower Raiju's cooldown, every change to his 1 is fine except for the decrease lower scaling and please fix that occasional glitch in his ult. Other than that, Raijin is fine and people just need to learn how to use him.