>If you run a P4 with modern distributions of linux, you're likely in for a bad time.
What universe are you operating in? I can run multiple domains worth of services just fine. Yeah. Compiling at -j4 at the same time can be a PITA. Running the desktop over X with compression over ssh works just fine as well.
The key to outpacing a pentium with a Pi4 is entirely dependent on structuring your workloads correctly. Given a heavily serialized load, a Pentium'll smoke a Pi 4 before it even gets it's britches on. Throw in enough parallelizable workload, however, and the Pi4'll pull ahead promptly.
If you run a P4 with modern distributions of linux, you're likely in for a bad time.
But if you take the time to customize a distribution of Linux for the hardware, you're not going to have much of an issue.
The biggest problem by far is the modern web browser is an absolute bloated pig.
https://www.sevarg.net/tag/raspberrypi/ has some hints and tricks.