This is always the case in anything in genetics. You may be onto something, but nature always culls... so you have to consider that. If you planted say four seeds in a two inch pot, and if they all came up you'd best cull some of them, probably three, so that the one that you wanted would be able to get the most out of the space. Now you could cull to keep thinner seedlings, or whatever trait you saw that you thought interesting... there is nothing wrong with that, and scientifically there could be merit in it. You could hedge your bets by culling some of your pots this way (keeping the thinner looking ones), and some the other way (keeping only the strongest looking), clearly labeling them as such and seeing the results.
what if the thinner ones actually have traits that would be good to have. Like disease tolerance, or healthier fruit. Idk, just some off thing you'd never know about.
Why in tomatoes is everyone talking about culling tomato plants?