As I commented in the thread I linked, a 1Meg resistor that is appropriate for ESD grounding wont help with the possible leakage current from a hot ceramic insulated mains powered soldering iron, as it only needs 10uA to develop 10V across the grounding resistor. It then becomes a matter of whether the peak voltage, low-pass filtered by the RC network of the grounding resistance with the MOSFET gate capacitance exceeds the gate oxide breakdown voltage.
Its even worse if you have an un-grounded SMPSU feeding a low voltage iron. The max Y capacitor leakage current set by various safety standards is 0.75mA, and even if the leakage is only a tenth of that, it will develop far more than any normal MOSFET's gate oxide breakdown voltage across a 1meg resistor.
Therefore, mains powered, and low voltage irons with a SMPSU that isn't specially constructed to avoid Y capacitor leakage current problems, need their bit hard-grounded to the same ground as the device you are working on (if its grounded).
Yes it increases the risk of ESD damage if you aren't working on an ESD dissipative surface, but you should be on an ESD mat anyway. If you are dealing with notably ESD sensitive devices, avoid working on a silicone heat resistant mat unless its from a reputable manufacturer and specifically was sold as ESD safe.