I mostly agree with you. Aang/Katara and Zuko/Katara shippers tend to be very different with the things they look for in ships, and Toph/Sokka and Sokka/Suki tend to be at least aesthetically similar. Added to that though is I think a certain unwillingness on Zuko/Katara shippers to pair anyone younger with anyone more than a few years older them because of a perceived squicky factor, and because it doesn’t really fall into their aesthetic sense of what is romantic. Also, because they like to dole Toph out to Aang as a conciliation prize.