Mine's reading temperature, humidity and pressure from sensors and uploading it to a VPS. My second one that is, my first one hasn't done more than collect dust.
Absolutely, ESPs are just microcontrollers. A Pi is a fully functional System-On-Chip. That being said the VPN is the only usecase you mention where you couldn't use a flavor of ESP.
Funny thing is that modern 3G/4G/5G modems are full System-On-Chip computers themselves supporting virtualization. The Qualcomm Snapdragon MSM8916 is a popular SoC used for LTE dongles that runs the modem Baseband Real-time OS and Debian/Android OS on the same CPU.
If you mean a Raspberry Pi 1, try RISC OS.
Very un-Unix-like, predates Linux by nearly a decade. Single-core and goes very fast on a Pi 1.
https://www.riscosdev.com/direct/