You're probably right about the currently known processes. But there are companies working on chemical engineering processes that are more efficient.
Here is one : https://hazer.wpmudev.host/about/#hazerprocess
Here is one : https://hazer.wpmudev.host/about/#hazerprocess
And the other points remain: we need hydrogen in other important fields (probably more important than cars, right?), so we should keep it there. If we get more efficient at producing hydrogen for those applications, that's good. No need to add cars on top.