I'm with John Smith on this one. In production, dowels are typically specified as a "drive fit"--0.003" to 0.005" oversized--and tenons are specified as a "slip fit"--0.003" to 0.005" undersized. I've broken production clamps intended for tenoned joints trying to drive dowel joints with them. It is hard to get sufficient force on a miter joint to close it if the dowels are well fitted to the holes. If they are loose, the joint strength just isn't there. Also, dowels are unforgiving. I'm used to holes bored with fixed machinery which gives more accurate location in end grain. Any drift of the drill will twist the joint. I love dowels for stuck and coped joinery, but it's hard to make them work with miters.