I don't think anyone is expecting syntactically valid code (or at least that would be huge red flag for me if I interviewed). You do get bonus points the more "real" and consistent your whiteboard code is though.
I think people dislike whiteboard interviews because there is a significant subset of people who do not perform well under pressure, combined with the fact that a lot of software development is not terrifically algorithm heavy. This means that it's a (by nature) uncomfortable task and does not adequately represent the value the developer can bring to the business. In my current role, I would much rather have someone who can show strong knowledge of dependency injection and unit testing on my team over the person who understands how to balance a binary tree from memory.
I really only use algo/code/sql whiteboarding for junior devs now, and most mid/senior devs get asked about some hard code bug they've solved, what their preferred software patterns are, and we whiteboard some architecture.
I think people dislike whiteboard interviews because there is a significant subset of people who do not perform well under pressure, combined with the fact that a lot of software development is not terrifically algorithm heavy. This means that it's a (by nature) uncomfortable task and does not adequately represent the value the developer can bring to the business. In my current role, I would much rather have someone who can show strong knowledge of dependency injection and unit testing on my team over the person who understands how to balance a binary tree from memory.
I really only use algo/code/sql whiteboarding for junior devs now, and most mid/senior devs get asked about some hard code bug they've solved, what their preferred software patterns are, and we whiteboard some architecture.