The Core i7-8750H CPU in the Dell runs 25 percent faster than the same CPU in the Razer Blade 15. The thinner Razer system does not benefit from Intel Turbo Boost as much likely to keep surface temperatures and power consumption in check.
https://www.notebookcheck.net/Razer-Blade-15-vs-Alienware-m15-Dell-has-the-major-performance-advantage.386516.0.html
Now if Dell could just design anAlienware laptop body that's isn't embarrassing for an adult to use in public I'd actually consider buying one!
The Razer blade has a gaming mode that unlocks the higher turbo and tdp limits.