Pretty hard to argue against radically different biological design between our brains.

I don't really see the argument.... For one, all mammals share fairly similar brain structures, with the main difference being the over or under development of particular regions of the brain.

However, even if we accept the claim that they are "radically different". A mere difference in brain structure does not preclude the ability to have complex emotions.

Yes, humans can be psychopaths and sociopaths.

I'm not sure if that's really relevant, sociopathy and psychopathy are defined by the subjects inability to conform to social mores. These terms cannot definitionally be applied to animals. However, there are plenty of examples of animals being shunned by their social groups, or animals who choose to stray from their social norms.

I'm not claiming animals share the same emotional capabilities as humans, but it's unscientific to claim that they are incapable of complex emotions based on the evidence presumed in this thread.

Imo there's been a bit of an overcorrection in science when it comes to trying to curb anthropomorphizing. And a lot of that is due to people like Thomas Nagel, who have a vested interest in stripping animals of terms like consciousness.