I was also left handed when I started school and I remember my mom told my teacher to help me shift to right. My had would be tapped with the pencil whenever I would pick it up with my left hand!
I became right handed but with my left hand still the dominant one, in most of my tasks like washing, pouring stuff, etc. I can still write with my left hand too!
My eldest is a leftie, I did not bother change his preference. I noted the second point on your article which is interestingly true with my son. He always suffers from allergies too. Hmmm. I wonder... 😞