The solution is to hire better designers, unfortunately. Savvy/wise/experienced ones know when to follow the rules, and when to break them.

Edit: That might not seem like the most helpful advice, and I'm sorry you have to deal with this – but it's the most effective, without having to write an entire book.

This book was written for industrial designers by an industrial designer, but I did find a lot of useful advice in here for designers on understanding the business mind, deferring to clients, embracing constraints and requirements, etc.

https://www.amazon.com/Designers-Are-Wankers-Neville-Brody/d...