This may be due to: The iGPU is made by TSMC 3N (SOTA power efficiency), the CPU is made by INTEL's less power efficient process node (same energy efficiency as in the predecessor), hence the battery life issue.
See the Panther Lake CPU Power Efficiency tests: notebookcheck.net/Intel-Panther-Lake-Core-Ultra-X9-388H-performance-analysis-Outpaces-Arrow-Lake-and-exceeds-Zen-5-in-efficiency.1212583.0.html
The ExpertBook Ultra is just barely over 1 kilogram and it can already run games almost as well as most budget gaming laptops over twice the size. Unfortunately, make sure you're next to a power outlet.