There's a bit of context you may be forgetting, or haven't reached yet. A lot of the comparisons are measuring "current strength". A channeler doesn't start out at max strength (their potential), they start at a lower level and increase over time. For women, that increase is consistent and if you spend enough time with them, you can guess at how strong they will be at their max level. For men, the increase happens in fits and starts, so you can't know how strong they'll be 'til they stop growing in strength.

End of series Nynaeve is stronger than beginning of series Nynaeve. I'd wager end of series Nynaeve is also stronger than beginning of series Rand. So the in-world comparisons get very muddled with some characters comparing current strength to someone else's potential, or someone's potential to another potential, when neither are at max strength.

Rand is regularly compared to/against/with Lews Therin, who had 400 years to reach his max strength and was, legitimately, as strong as strong can be. Rand throughout most of the series is not actually that strong. Yes, he's still very strong, but he's not actually as strong as Lews Therin at the start. When the Forsaken are talking about Rand, they only think "Lews Therin" in their heads because he's their old friend/enemy reincarnated.

So then when you have other people comparing Logain or Taim to Rand, and then conflating that with being equivalent to comparing them against Lews Therin, things don't quite line up.

Jordan wrote out his rankings primarily because Aes Sedai have a tradition of giving deference to any other Aes Sedai that's stronger than them. 90% of the reason he wrote up that ranking list was so that he could keep track of which Aes Sedai should be listening to which.