You do realize that you can hardwire to the same circuit the 14-50 is currently on? If the location is convenient, you can mount the wall connector directly over the wall box. Otherwise, after you remove the outlet, replace the cover with one that interfaces with conduit fittings. Use some hard or flex conduit and #6 THHN wire to run from the box to the wall connector. Use Polaris connectors to splice the new wire and the existing feed in the wall. Cap off the white wire.
Personally, I think that using a 14-50 pigtail is perfectly adequate. There are plenty of off the shelf EVSEs that connect in exactly that way.