We will have to agree to disagree on this 
 
Bypass thermostat set ups provide a more consistent operating temp (which is set by the opening temp for said thermostat) for a given engine.
Online thermostats have a cycle of hot-cold-hot-cold as the crack open and close again during the coolant cycle.  Dropping engine temps, closing, increasing engine temp and repeat.
Bypass systems trickle flow the block/head(s) providing more consistent temps inside the engine.  This is both more economical and more efficient.
The heater core is used to maintain bypass flow as it prevents nucleate boiling by allowing some consistent flow (the heater core also assists cooling, it is a small radiator after all).
As Slunnie posted, a side benefit is quicker heater activation and quicker engine temp build.
When I built high performance vehicles, we would deliberately remove the block mounted thermostats and replace with inline bypass units to improve thermal efficiency and cooling.
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