Your designers are going to be looking at the layout; they're not going to notice if it's slow, uses too much memory, is not maintainable, doesn't follow repo patterns, etc.

Do you think it is reasonable to expect a person with an arts degree to know this?

This isn’t meant to be sarcastic: have you ever worked for a real company?

As we know from THERAC-25, etc., comprehensively verifying that code works the way it's expected to is not actually very easy - it's perhaps one of the hardest parts of building any system more complex than a toaster.