Ah right, that's a bit disappointing. But I suspected this would be an issue when I read
Up to 23W for compatible Pixel phones.
In that case I'm guessing I might as well go with the Pixel stand 1. Mainly want to use it at night by the bed so I don't need to think about the cable. So the super fast charge really isn't that important.
Would be interesting to know if this is fixable or if it's too deeply integrated in stock OS in some way.