Betta Fish: Do runts stay runted?

Question for the betta masters; will a stunted fry stay the runt? My friend and I had some spawns of Bettas near the end of last year, I didn’t have it in me to cull any of the off base ones and I’ve gotten some great colors, and personalities along the way. Most of this little one’s siblings have been grown and permanently homed for a few months now. There were a few smaller ones, I separated them once

I noticed they were abnormally smaller and getting picked on. The others have grown, I can sex them, etc but this one’s just been stuck in time.

It’s alone in the tank, it’s a small 5 gallon nothing fancy. Diet seems healthy, it will always try to eat the biggest piece of food and follows scuds and hunts them. Water temp is about 79-81 on average, soft water filtered through RO in a planted tank.