I don't think its perfectly correlated at all. Firstly, we know that it's a Talent, which means that by definition channelers display varying aptitudes with the weave. Forgetting even outliers like Androl and Berowin who show extreme forms of the Talent, we have seen that Aviendha makes smaller gateways than Elayne despite having very similar strength in the Power. If we knew nothing about the two channelers, we would mistakenly assume that Elayne is stronger in the Power than Aviendha.

I do agree that there is a strong correlation between the two. Logain has obviously seen enough Ash'aman weaving gateways. He makes the biggest gateways and he's also the strongest Ash'aman. Rand makes a bigger gateway and is also stronger. However, we don't know if Rand's is proportionately more. Rand may be 5% stronger than Logain but because he has a strong Talent, his gateways are 20% larger in area. Conversely, Logain may have a weak Talent. Most Aes Sedai can only make a gateway large enough to put their arms through, but they aren't a hundred times weaker than Rand. The relationship is not completeley linear.

The stronger you are in the Power, the bigger your gateways. There is no doubt of that. But you can't extrapolate strength from a gateway. If Demandred saw Androl from a distance he might think that he is very strong in the Power, but it is a poor assumption which I don't think he'd make in the first place.

And because we're discussing strength in general, remember that it takes roughly as many women to hold Rand and Logain. Their power must be close, especially because Logain tried to break free and five women almost lost the shield.