REG_ORIENTATION_SETTING
DEFAULT_STYLUS_CONTROLName some?
Granted I’ve been out of the homebrew dev scene for a while, but this doesn’t sound right. Developing for Windows CE would require a commercial/proprietary copy of Platform Builder and Dreamcast BSP. This is not very “homebrew” friendly at all - especially when there were a ton of homebrew libraries and OSes for Dreamcast through the years, eg Kallistios.
Modern titles like Intrepid Izzy I don’t think are WinCE though.
As for performance, having an OS instead of coding to the bare metal of course imposes overhead but, from what I recall hearing, 3D performance of the WinCE SDK was on a par with Sega's SDK. The graphics engineers had access to Sega's SDK so they were able to do their own comparative benchmarking and they knew game developers would be scrutinizing that.
Ultimately, SR2's frame rate was entirely in the hands of the Sega Rally 2 development team by what code they used and what level of detail they tried to show. The cheat code for SR2 for the Dreamcast that reduces detail to increase framerate is an example of that. They were highly motivated to replicate the arcade experience as closely as possible and constrained by a need to hit the launch date and made choices that resulted in the frame rate issues SR2 has. Had they been using Sega's bare metal SDK, they may have made the same choices favoring arcade fidelity over stable framerate and therefore laying all the blame on WinCE isn't entirely reasonable.