My main issue was less about how they looked and more about what they were capable of. The idea of being able to essentially species change a Klingon into a Human with TOS-era Klingon medical tech sounds impossibly advanced for what the Klingons are known for. Their scientists are few and far between, and even in TNG it’s elaborated on that treatments for disabilities aren’t even looked into, they just tell you to kill yourself. That doesn’t sound like the kind of species that 100 years prior is going to be able to do this insane medical procedure.