Really, we are working with a population. We are trying to move a population of birds forward. We think individually, and we should. It is a trees and forest thing. We do not want to neglect either. So in terms of a population, we are looking at an average. Removing the bottom performers drastically improves the average. Doing this alone is maintenance. You have many points to consider selecting your birds. At least identify and remove the bottom performers, cull eggs, and try to emphasize the birds that excel. If you do nothing else, you have been faithful to what you have to work with. The strengths and weaknesses of strains will vary, and they should.
This year the pullet eggs from the breeding pen started out larger than last year. That seems like a good sign. I was able to select the breeding pullets better for type this year, for one thing. Also, we've been steadily improving our management of the flock, and I can see that in improved shell quality on all the eggs, even from the spent hatchery hens we just "retired" to the auction. My breeding partner/mentor, @Zanna , she has more experience selecting for type, and her pullet eggs have been enormous.
I'm probably repeating myself here, I invested in some hands-on help & training from a local breeder who is also an APA judge. I highly recommend that. We've all enjoyed working with him. It's great to take the stuff I learn here into the coop with a qualified guide so I can apply it.