You're absolutely right—most modern laptops, especially those made after 2013, have their CPUs soldered to the motherboard, making upgrades virtually impossible. This is especially true for high-performance mobile workstations like the ZBook, Precision, and P series, which use specialized components like mobile Xeon processors and require significant cooling systems due to their higher TDP. These machines are in a different league compared to entry-level models like the HP Pavilion 15-p, both in terms of performance and price.
While the allure of a Xeon/FirePro setup with a high-end 4K display is strong, it’s important to remember that these systems come at a premium, whether new or used. Even finding a deal on a used ZBook with such specs often means compromising on something, like dealing with an unknown BIOS password or other potential issues. It’s a trade-off between getting top-tier performance and handling the challenges that come with it. If you can find one at a reasonable price and are prepared for the potential hurdles, it could be a great investment, but it's definitely not for everyone.