I would caution people against taking SOLID as a measure of code quality. That’s a trap. SOLID is just a set of object-oriented design principles, not laws. If you take the guidelines too seriously, you will end up with a damaged code base which is difficult to read or understand.

Having spent quite some time in id Software code bases, I will defend them as being high quality, but whether or not they are SOLID is not something I really care about. The SOLID guidelines also regularly conflict with YAGNI.