For what it's worth, and to be fair, I am not in a guild that can complete CRancor, or even come close, but just as an outside perspective, it seems to me like this change is going to make teams less effective when the boss has no %health buffs, and more effective once it gets down 20%, but certainly by 40%. The complaint in this case then is that the raid is guaranteed to be more difficult than it was previously, when all attacks per phase were being done at the same time, so there was never any buff. That is a valid concern.
However, that also required extreme coordination, and often guild members holding one attack in airplane mode for sometimes as long as 8 hours. It is not fair to expect that the need for coordination would go away but the raid would stay on the same difficulty. That defeats the entire purpose of the raid being a guild effort.
There is the obvious concern that some guilds who were relying too much on a few teams will no longer be able to beat the raid, and that is in some respects a problem, but it also reflects on the idea that raids were designed to be a guild effort, even if excess timed coordination was never part of the puzzle, and you should not be able to beat a new raid with only a few members. It's supposed to take most of the guild. Any guild that was beating the raid with full participation before will now most likely find it easier to beat, not harder. Therefore, this seems like an improvement, as it rewards completing the raid in a way that supports guild participation and support.
That being said, an adjustment of the rewards is also required. At the moment, there is no incentive towards anyone in the bottom half of the guild to put in a considerable amount of effort, time, and attempts to get negligible rewards, while the top half gets all the goodies. If only this element of the raid is changed, but the rewards do not become more balanced, this is not a good solution.
