Hi,
I managed to find the reason!
If i set my columns programmatically, and I have a column that's hidden, and it's width is set to 0 or no width parameter at all, then rendering is 3-4 times slower on Chrome, and about 1.5 slower on Firefox
You can test it here:
https://jsfiddle.net/xwyq3ehd/14/Run the script, Click Load, Watch the time.
Then change the width value on the first column to any number, Run the script, Click Load and watch the time again.