The issue is that handhelds are limited by their batery capacity. Running a steam deck at full power will exhaust the battery in ~2 hours. The ROG ally X outperforms the steam deck, but at the expense of nearly 2x battery consumption (25 watts vs 15 watts). You can't even run the ROG Ally at full power unless plugged in. Valve is probably waiting for efficient processors to make a significant leap in computing performance at the same TDP.