Dwyer's worth outside of the Castle is pretty low when there's a lot better options for healing.
As for Iggy, he is good at tanking if paired up, but to be fair so are almost all Generals/Great Knights on their own. His personal skill also hurts him a lot when not paired up. But if you're the type to always have him paired, then he's a good meat shield.The biggest problem he and Benny share is that they're both inferior to Effie. You could argue that Iggy is better if paired up, but the fact he has to be paired up to tank better is reason enough when Effie can be on her own and still kick ass.
But if you want my opinion on worst child, it's Asugi.