I got told different advice by different doctors about both my sons, who at the same age were the same weight.
I got a second opinion about my first son, who I was told to wean, and was told NOT to wean. Went back to the first GP and advised them what I had been told, and she shrugged and said at "this age" (4 months) she recommended weaning no matter what the baby's size. The second GP was horrified and insisted I wait, and told me that not every GP is up to date on guidelines-- and this from one GP about another. Is that not proof doctors aren't God and they aren't always right? Obviously, I stuck with the opinion of the second GP.
When I got referred to a paed for my second son, they told me to wean as breast milk wasn't enough and he didn't "weigh enough", in spite of the first physician I saw, and then the second, telling me he was fine. It turned out my HV, who had referred me, was telling the paed that I "starved" my son on breast milk, and because I wouldn't FF, she was "advising" I wean, and the paed agreed based on her "notes" (which were all basically bashing me for BFing as my baby was so "small" and he needed "more").
I am 4'10" and 42kg on a good day. My sons were 5lb 3oz and 5lb 1oz born. They weren't going to magically become 50th percentile babies as soon as they were outside me. Still, the paed listened to the HV and it kicked off a heap of shit I just didn't need. The second paed I saw, told me my son was just little and what was I doing thinking of weaning when he was nowhere near ready?
Did I mention my sons followed basically the exact same growth pattern, right up till 1 year, when they weighed exactly the same? Two babies, same size, different advice from many professionals-- and I can tell which ones researched and which just blindly "believed" early weaning solved all because in "their day" that's what people did.
My point is, is if even health "professionals" (I use this lightly about HVs, since they are included in my story above) can't agree, why not err on the side of caution and pick the safer guideline of 6 months? It's been researched and wouldn't have changed from 4 to 6 for some flimsy reason. Science backs it up. Anecdotal evidence, as well as "in my day", does not.