You can take this for what it's worth, a Duramax will not run properly without a functioning MAF sensor and won't run to it's potential without it functioning properly whether it's in the wrong location, scaled incorrectly, dirty, bad whatever.
Just like any computer controlled engine it relies on the sensor inputs to calculate the fuel pressure, fuel quantity, timing, etc.
If you "Dummy" a sensor or simply disable it by telling it to "Not Report" you might get away with a No-MIL but you still did not fix anything.
I like to say you fixed your "leaky roof" by placing a bucket under the drip, the drip is still there but the leak isn't getting the floor wet. Instead of emptying the bucket why not fix the roof !!
MAF is probably the most critical sensor besides ECT as it has the most effect on the engine.
I hope you figure it out, if you choose to ignore the MAF then you might as well forget about it running to it's full potential.
Just my $.02