“Part of that difference is because HP insists on limiting clock speed to 4.5 GHz, even though the 7840HS should be able to boost to 5.1 GHz.”
AMD built Phoenix with eight Zen 4 cores, RDNA 3 graphics and 25.4 billion transistors on TSMC N4. Then HP shipped it in a laptop capped 600 MHz below its rated boost and paired it with slow CL46 memory. ASUS lets the same silicon hit 5.1 GHz in a handheld. The spec sheet sells you AMD’s chip, and the OEM decides how much of it you get.