Data point from Air Canada (I have found BA to be reasonable with minor variations up to a kg without any pushback as I weight my bags at home and pack each bag according to published rules).....for giggles....checking in at YVR domestic during covid...I was ..15 kg over on one bag....told to repack.....told that automatic scale would not accept anything over...could not manually be overriden...took out box of cookies I had packed for kids and ate a few and offered a few to fellow travellers. Stupid quite frankly and while it left me rolling my eyes...pretty much sealed AC ever receiving further business from me...only reason flown was it flew a route that was not being serviced during covid.