For highly hopped beers, yep totally agree, but for more traditional ales / pale ales like I tend brew then I have never had any issues with oxidation, CO2 is heavier than air, so I believe the blanket of CO2 produced by the yeast should sit in the bucket and protect it for a couple of minutes, I think the risk is so minimal..... and many beers are brewed in open fermentation vessels in the traditional commercial breweries.
Doing it in the fermenter does leave the crud behind and the trub is very jelly like and compacted after you transfer, but I don't think that is any advantage / argument for doing it in the fermenter.
That said, I like the idea of adding to the keg before you transfer, whether you pressure / closed transfer, if you can do it that way with similar results, then why take the risk.
Always learning and adapting the process...