Much like a 'born again' Christian is delusional? I mean, really, you can only be born once. /S
Your definitions are wrong. Modern medicine holds that gender is identity and sex is biological.
sexes - male, female, intersex
Gender - man, woman, non binary, gender fluid, etc.
If you want to call someone delusional who's gender and sex don't match, you are free to have that opinion, but pretending that you don't understand what the person means is just lazy.
Most people who pull this argument think trans people are immoral and/or mentally ill. If that's the case, just say so instead of attacking vocabulary.
If you think they are mentally ill, describing that illness involves gender and sex.