other examples are Tormolen in "Naked Time" who casually removes the glove of his isolation suit to scratch his nose
Actually, we have no evidence that this would have been an "isolation suit".
When Spock and Tormolen beamed down, they did not yet know that there'd be biological or chemical agents down there threatening them. They had no reason to suspect such a thing. They did know it would be hellishly cold down there, though. So more probably, those were cold climate suits, designed solely to keep the wearer warm.
After all, note that the suits do not provide any isolation. The headpiece is separate, in no way sealed to the rest of the suit - air is freely flowing through the neck area. The gloves aren't sealed, either.
Perhaps this is a standard issue thermal regulation suit, used in both cold and hot climes, and in fighting shipboard fires? The ability to quickly don it would then be paramount.
Timo Saloniemi