I honestly don't know how the normal tank raid difficulty was before or after the nerf, but I generally want to know why you're putting so many rules in place to begin with.
For us, we have a preopen that can be 24 hours but sometimes comes after our reset when we have enough coins. We raid at the same time every day (provided the tickets) no matter what. We preopen so people can log zero damage. Then, when it's raid time we zerg the rancor in about 15 minutes (depending on how many show up) and tank in about 50-53 minutes (again, depending on how many show up). With the zero damage, everyone can at least log something to get rewards.
We do not ever limit how much damage or how many attempts someone does. Our raids go fairly fast. If you snooze you lose. I've missed out before due to real life. It happens. But we do not limit people and we have set times that everyone knows and follows otherwise no rewards.
Granted this is for heroic raids. I still don't understand why you would impose so many rules for normal or anything under heroic. If members don't log damage that's on them. Don't limit other people. That's how you lose members.
