I have to say the OSK is a terrible work around. Mainly due to the extra key section that seems unnecessary for touch input. "pg up", etc. section makes the num keys basically useless. Your screenshot is a great example. Second reason is that the keyboard isn't really locked down and accessible like the touch keyboard is. It doesn't naturally call up and hide as you engage in typing and then finish.
Generally the touch keyboard and Microsofts implementation of it seems to be low priority. It's not optimized just seems tacked on. It is undoubtedly the biggest weakness of my new Surface Pro 9. I have a feeling it may make me grow to hate using the device. Throughout recent history, physical and touch keyboards design is pretty important as they can make or break the success of a product. Think Blackberry Storm Vs iPhone. Think Apples first few years with the MacBook butterfly keyboard. VS the Dell XPS. Surface is starting to get some pretty good competitors both on Android and Windows. I think they need to really push forward with a new innovative touch keyboard that is optimized and scalable.