Re your example of crossing a hen laying a smaller egg with a rooster breed that lays jumbo size, yes your example is exactly how i've increased average egg sizes/weights. (I know my home-hatched roos Also hatched from good size eggs). It took several years/generations to get average egg size to xlarge, but i saw noticeable improvement each and every year. I simply chose the biggest (& most colorful) eggs to give to broodys to incubate. It's lots of fun selecting the eggs, & is hard to choose since so many are now big and pretty!
The reason i mentioned all the above is because you commented on your current four lav orp eggs in the incubator being 52 grams or less, & one being slightly mis-shapen. I understand your disappointment there, & that is exactly the situation you can avoid by choosing your own hatching eggs. How far along in incubation are they now? Hopefully they will all hatch. But even if they dont, the entire process takes at most 3 weeks. Meaning you can soon try again.
Btw i do have several lavender orpington hens. I Love them! They are extremely friendly, curious and sweet, & follow me around everwhere. And they are very beautiful too. Ive read some people say lav orps are "over-rated." I will say, mine dont lay as many eggs as most of my other breeds, but because of their positive attributes i dont mind. Love my lavender orpington girls. (My lavs are Much more friendly than my buffs.) I think you will love yours too!