Whiteboard coding is nonsense for any other purpose than weeding out the truly incompetent.
Past that point, it's a crapshoot. I think homework / portfolio are the most reasonable evaluative tools, but there are some legitimate downsides there around the bias it can introduce into your process, and the potential candidates who may be turned off by it.
Things worked out for me, but not before I had some serious self doubt.
So, stick too it. You (probably, I don't actually know) are good at your job - don't let the nonsense process convince you otherwise. Look for companies that share your viewpoints.