Perhaps they're all close in raw strength, and perhaps they're not so close as that. The fact you guys still argue over their strengths after 13 books is because we don't have enough information to be certain of anything. And one of the main reasons we don't is because the Chosen themselves tend to factor their raw strength advantages or disadvantages for much, much less than third age channellers whose knowledge of the OP is minimal and forcing them to rely on simpler tricks most often dependent on raw strength.

The Chosen come from an Age where personal angreal and mixed gender circles were common place. None of them is stupid enough to rely primarily on strength when they've learned to fight in a War where a woman like Lanfear might have to fight for her life against a much weaker underling who suddenly acquired an angreal. They've all learned to rely on their best skills.

Raw strengths comparisons don't come naturally to them the way it does for third age Aes Sedai. Some of them might be very close in raw strength, I tend to think there might be some gaps larger than we think, but I think the differences whatever they are aren't very apparent anyway, far less than among AS, because they all come from the same crucible of pre-Collapse full Aes Sedai training, while OP knowledge vary a very great deal more between third Age channelers (groups, ajah, individuals keep some of their discoveries secret). Not only that, but they've all fought in the same war, picked up a lot of the same tricks developed for destruction and fighting other channellers.

We see this reflected a lot in the series. It's in their vastly superior knowledge and skills the Chosen systematically glorify themselves with (and they're keener to compare their special skills, their non-OP related skills and weaknesses and their respective cunning than anything else), while among third Agers, it's the raw strength of the Forsaken they find amazing and intimidating... They push this to the point of absurdity, like believing that the Cleansing was the female Forsaken working together...

We see the Forsaken barely ever referring to their respective strengths. They know all thirteen have pretty much the same basic knowledge and training, and all of them have learned to use their best skills rather than rely on their strength. In the pre-Shadow days, they wouldn't have let their strength limit them, they simply had to use an angreal at need. Even Lanfear knows better than to count on a gap between her and Graendal, Moghedien and Mesaana, when that gap might be filled at any time by an hidden angreal.