Like this chapter shows, the Calamities like King and Queen fight by constantly switching forms the former due to not having a special fighting style, the latter due to being a cyborg, all using their arsenal depending on the situation.
Like in this chapter for example, there is not much difference between hybrid Queen and full zoan Queen in terms of perf. He arguably even did better in full zoan form than in hybrid, switching to full zoan form to ultimately crush Sanji's bones
And it was similar with Jack whose hybrid didn't perform any better against Inuarashi, so at this point I think Oda just switches the forms depending on what he thinks could be suitable for one or another situation