As quick as I am to criticize the bizarre versions of Christianity, I do think you're in error to assume Pentecostalism is all or even mostly about "planned remarks passed off as spontaneous".

Improv is a thing, and can be trained as a skill even outside of comedy/entertainment.

Though, outside of Charismatic sects, Christianity does see a more reasonable level of "I had prepared by thinking about (verse X), but suddenly now I'm thinking about (obscure verse Y)."