Opinion or fact?
Water conducts heat better than a glycol/water mix.
Water will Transfer heat better than a combination of glycol and water up to its failing point.
Water will freeze at 0c and boil at 100c, a mixture reduces water vapourization compared to without because a glycol based mixture will not boil and therefore not steam.
A plain water application if it gets to 100c will boil unlike a gylcol based coolant. So glycol mix controls/manages/stabilizes heat more effective to a higher temp as glycol based coolant can handle higher temperatures.
Glycol mix will evaporate eventually when it gets hot enough, but it will evaporate slower than water. Water will leave you with no protection against scale exess heat, corrosion & oxidation.
If something does manage to fail in the system the gylcol assist with higher temps and would avoid boiling unlike the plain water.
A 50% glycol mixture will increase from 104c+ to even higher, efficiently eliminating the 100c water boil also it vaporizing leaving a hot air pocket that will enevetably cause damage as a result of not cooling a affected area trapped with stem/air. If water boils it vapourizes, evaporates leaving a hot air pocket not cooling.
Water boiling at a lower temp, creating evapouration also vapourization of the total water amount, is reduced over the duration of operation leaving areas within the system without water transfer properties.
A radiator should not get to 100c to boil unless there is a failure in the system in that case a failure is likely to increase the temperature to above 104c which a gylcol coolant would handle.
My car stays cool during the Australian summer.