Well, I don't really see it as a problem, as you get a fair amount of wiggle room with your defensive actions. Say somebody charges at you, and bypasses your zombies, you could in theory still do things like shinra tensei, and such to drive them back, while still causing damage.
Is that not 'defending into the motion of an attack', Trev? Well, that example is a flat-out attack if you think about it. All the enemy is doing is running at you. Maybe he wants a hug lol. But on a serious note, you should see what I mean.
Well, the point of nerfing it was to take away a large part of its strategic value; it is one thing to have summons in battle (that now I have to start counting, as apparently they do have a bit of a time limit, though it seems long) but another to have another shinobi on the battlefield. Hardly anyone wanted to have to deal with two shinobi vs one (except maybe people like Kirk and Zenaku, who would take it as a challenge).
It's one thing to nerf a technique, and it's a whole 'nother ball game when you're killing a technique which is what this rule does. Technically, with summons being able to perform various assortments of jutsu like transformation, and use the advantages of said transformation, what's stopping them from being another shinobi, as transformation is a really cheap jutsu as we all know. There's virtually no difference in it. (And yeah, fighting 2 on one would be friggin awesome!)
As for the 20 percent loss, it would make sense to be a bit winded considering the sudden drop in permanent chakra. That's not like splitting it up with kage bunshin or anything because that chakra is completely gone, ya know? That's just how I see it. We all know how few people actually deal with chakra exhaustion, but that's beside the point. It's still a nice chunk of chakra gone.
The no attack method is also rather bad for everyone else because this rule encourages the user to summon more zombies out because there's almost nothing else that the user can do while using the zombies. Think about it like this, what would you rather fight? 1 human + 1 zombie (unless the user is dumb enough to waste all of their chakra on three zombies, leaving them fairly useless. I don't care how much chakra one has, you are NOT fighting as well at less than 50% chakra) or 3 zombies while someone lies away with attack prevention or kamui, being completely invincible from life since they can't do anything else with their precious chakra.