Chris stopped going after Leon, cause he's a MASSIVE SIMP, (Endangering and sacrificing thousands of lives for allowing Ada to live on, getting chris' platoon killed, stealing several viruses etc. cause he "Loves her" despite she literally using him as a puppet) his genes are tainted because of that...Ethan however... is a total chad that went through hell, (lost his limbs, had them reattached, figuring complicated puzzles) and kept going for someone he cared for (Redneck torture family, Chainsaw Duel, flaming a moth chrotch, Icing a gigantic sludge monster, and soon enough going thru Yharnam Lite), and he didn't have any training or special ability, he's just a regular man, with incredible willpower and the perfect candidate!