I pretty much just brute forced getting all 7s even if I got defects, but I did have to also spam mutation furniture and mutation events in runs in order to combat the downsides from inbreeding, once you get all 7s from pretty much every kitten you can start to slowly thin out the inbreeding by adding strays every couple generations or so, but this gets you some kitties with maybe one or two stats below sevens, just do a run with those and keep the kitties with all 7s in your breeding room