But there is a correct way of speaking in English if English is the native language and IMHO, to drop the "h" from words and pronounce "th" as "ff" or "v" as in "Portsmuff" and "wiv" sounds unprofessional and less authoritative.
Well, I think that we will have to agree to disagree on this. It certainly sound less refined for cabin crew to use estuary English turns of phrases or pronunciation and therefore may affect the image that the airline might want to project but that would not lead me to doubt the professionalism of the individuals concerned. It simply is not an issue of professionalism.