What consensus do you refer to w.r.t. the 300 hrs for BA FPP? That would certainly be news to a few chaps on the programme with significantly greater than 300 hrs TT. I suspect you've been talking to ex-cadets from the 90s, for which there was such a restriction.
I don't know anyone who would frown on a PPL experience; however, there are plenty who have no experience before starting an airline-tagged cadet course.