Thank you for sharing your experience and insights. It seems that the debate where designers should code is still contentious as ever.
I understand that that as an engineer, it would be frustrating to deal with the below scenario as you describe.
Developer: Yeah, this can be done, but this it will take some extra time just to make sure that this drop-shadow will work cross-browser.
Developer: Do we really need to do it this way?
However, I would argue that here is a great opportunity for the Developer to provide suggestions for the solution, as well critique the designer’s work.
The designer can obviously learn to contribute through code, but as engineers would have more knowledge in this area, it would also benefit for them to understand how designs can add context behind the work they do, particular if that dropshadow helps users complete their tasks successfully.
All in all, here is where co-design is key, between developers and designers. Everyone has a responsibility towards delivering a good design, and I’m sure if the right designer work with you, they would be open to your input, because it would make their life easier as well.