Plant body

Each plants different from the next same as each person is different from the next environment as alot to do with how they grow and I have found without the full equipment and decent seeds then results are useless growing and getting good results isn't easy and takes time to learn just like anything else happy growing get the environment perfect and good seeds and you can get nice results but there's plenty of hurdles to get over before you can expect good yealds with decent amounts

Okay so the real answer is yes there is Genetics. Just your substrate makes a massive difference in plant size. Coco, or Hydro will get much bigger faster then soil. Soil is really hard on autos. Living soil if insisting doing soil is best for autos. Other then that Hydro will give you a great result

Every seed contains their own generic or phenotype, just like you're siblings share genetics but look and act differently, it is normal, sometimes a pain but totally normal