I've read a huge number of first-person accounts of WWII air combat. Sometimes, a pilot does tell you that things done with prop pitch, mixture, throttle setting, etc. But often, those were things that a pilot did when first entering combat from a cruising configuration. Then, once in fighting configuration, they aren't doing much other than manipulating throttle as desired for combat, usually keeping it on full, less commonly chopping it to slow down. Cowl flaps were usually staying closed. Oil-cooler flaps are usually on auto or in some state that don't require manipulation during a fight. Mixture in auto rich. Prop in max rpm. Mixture and prop are fiddled with in cruise. The other various flaps are usually fiddled with in landing and takeoff.
You just described exactly what DCS engine management entails in combat. Manifold pressure (aka throttle) and RPM are the only things that really change in combat. For aircraft like the P-51 there is even a placard inside the cockpit that lists manifold and RPM settings for different regimes of flight.
There seems to be a fear about engine controls in IL-2 and DCS. In DCS you have several options:
You can press a keyboard command (or map it to a HOTAS button) for "auto-start". All the correct switches/levers will be activated for you. You just sit and watch the engine come to life.
You can do a "hot start" in a mission. The aircraft and all the major systems are up and running when you enter the cockpit.
You can do a "cold start" where you activate the switches/levers in sequence that is outlined on a kneeboard checklist. For me this provides the quickest cockpit familiarity when I learn a new aircraft. There are cold start training tutorials in DCS that take you step by step, giving you a description, pointing out each switch/lever, and proceeding to the next step once you have correctly activated the control. It really is spoon fed to you.
For the P-51, once the engine is started you can simply click two switches for the oil cooler and inter-cooler to "open" and you are good for taxi, takeoff, cruise, combat, and landing. For the Spit9 you don't even have the two switches to activate.
I imagine IL-2 is similar.
