As a gamer in a game design club, the issue of simplification of complex games resulted in constant discussion. Usually the discussion was between realism vs simplicity. My answer is always the core of gaming: Quantification.
What is quantification?
The expression or measurement of the quantity of something. Every RPG is a quantification of PCs, NPCs, situations and monsters.
As a wargamer, the games existed because combat unit capabilities are estimated and quantified for gameplay. We can refight the Battle of Waterloo because we have an accurate idea of the units involved and contemporary impressions of their quality to give them other than a rating in combat of "Average" in some cases.
Avalon Hill, a maker of wargames since the 1950s used a simplified chart (Combat Results Table or CRT) in almost all of its games.
From the CRT, which also has another table to calculate numbers before hand calculators hit the market, you could roll the results of a battle between units using 1d6. Simple and clean.
When bored, my fellow gamers made a fast and simple game of Russian Roulette: roll 1d6, on a 1 you blow a hole in your skull...and lose. It didn't have the pressure of using an actual pistol (I was a VERY bored teen) but was an example of simple game design.
Want to speed up a game? Quantify the known elements and make a chart to determine possible outcomes. I say "Flip a coin if you want a simple determination." Pass/Fail is as simple as you can have. Battle of Waterloo? Flip a coin. Balrog vs Gandalf? Flip a coin. Frodo vs the Ring?
Flip a coin. Easy.
Conan vs Horde: Conan can take 10 hits before dying. Flip coin. Heads: 1 (Insert enemy here) dies; Tails: Conan takes 1 injury; Simple.
In a GHQ wargame, all the units had a point value, every tank, jeep and platoon of soldiers could be bought with allotted points.
In a particularly dull afternoon, the GM says, "How about a pick-up game?"
Gary: "No way, Vlad always beats us."
Me: "How about I let you use
German units with
double the points?"
Background: Gary and Mark are nicknamed "The Laurel and Hardy of microarmor" in our club...for good reason -They never coordinate, even though they have a better than average grasp of unit capabilities. Me: 82nd Airborne, sergeant; Ed: 5th Infantry division, sergeant...
Gary: "Sure!"
Ed: (Looking at me...) "You are so evil."
After action: The tabletop is 4x8 feet with a small village in the center, where roads intersect. Ed takes the Infantry and artillery assets, deploys the artillery and speeds up the road into the village on Turn one.
Turn 2: German units cautiously enter the opposite end of the table at cross-country speed, mostly infantry in halftracks and towed artillery. Me: Tank destroyers and tank hunter infantry teams speed up the road to deploy among a line of hills overlooking a secondary road into the village. Ed deploys his infantry in the village and take up positions in the buildings.
Turn 3: Gary enters the board with a company of Jagdpanthers, lined up on the road my tank destroyers happen to be covering. Two of the lead vehicles, Panthers, speed into the village...
Turn 4: The two Panthers in the village are attacked by infantry, one is destroyed immediately by a bazooka and the other crippled. My TDs open fire and destroy half of the Jagdpanthers on the road. Bazooka fire from TH teams erupt from positions near the column and Gary turns to face the TDs in the hills. Ed spots Mark's halftracks from the village and calls artillery strikes. Mark's commander dies, Gary's commander was in the lead Panther... The German SS infantry retreat off the table, with heavy losses.
Americans lost 2 men.
Flip a coin.