I am not a big fan of comparing different era's. Batting and overall cricket is much easier now than it was back in the days. The value of a 100 rupee note back in 90s was much higher than what it is now. If you had invested that 100 rupee in a stock, its price would be in thousands now due to its appreciate value. Similarly runs scored back in the day had much more value than what it is now. It is just the law of nature...everything moves on in life. This is the same reason I don't go gaga when people say Kohli is just 1 century away from Tendulkar's 49th ODI hundred's. Tendulkar's 49 ODI hundreds is probably worth 80 in modern era. On topic, Gilly was a much much superior cricketer than De Kock.
It is just my personal opinion...so De Kock fans pls don't come after me.