AFAIK that 3A figure for the Pi includes power for the USB ports on the Pi. So if you don't load up the USB ports, you can get away with more like 1.5-2A, depending on what you do.
FWIW my 4GB RPi 4 pulls about 1.2A peak when using the CPU full tilt. Haven't stressed the GPU yet so don't know about that. This without any USB except wireless Logitech keyboard/mouse receiver, and with Wifi enabled.