I see a few flaws in your interpretations:



Elayne isn't even close to being able to use the Bowl on her own (at least, not for what they intended to do with it - the ter'angreal was actually designed to control the weather in much, much smaller areas).

She doesn't really know how strong a woman has to be to make the bowl work, she's guessing. Part of her problem was that she didn't have the skills to operate it properly...

Herself isn't quite strong enough (she thinks), so forcibly all the Salidar women aren't. She wonders if Nynaeve, who is significantly stronger than Elayne and Egwene (this was confirmed by Brandon, by the way), might be strong enough.

Elayne is merely guessing at the strength needed to power the Bowl (and as it turns out, they will overpower it and overwork the ter'angreal, making the OP "weird" in the south for a while. The Bowl didn't need that much OP to work, it wasn't designed to create so global an effect on the weather)

Let's assume this is very close for Nynaeve since she has to give it some thought before she says she can't do it... so perhaps Nynaeve's maximum is between 480-500lbs.

The whole episode is very unreliable for comparison, as Nynaeve didn't have access to her full strength. She had access to a limited quantity of saidar from a well, not renewable. She wasn't guessing if she could lift that weight in th absolute, she was guessing if she had enough saidar in her well to do it, keeping enough for the rest of possible emergencies. She had to ponder that decision well. If she tried and miscalculated, she emptied her well... That's why she hesitated and finally judged this wouldn't work. I'd assume she has a good idea already how much she can lift when she has her full strength. In Far Madding, she had to re adjust herself, because Nynaeve isn't used to work under limitations of strength. She has more than enough strength to do pretty much all she has tried to do.