Simple for you doesn't mean simple for other people.
Without writing down the steps on exactly how-to use the older icons, it doesn't equate to simple in my opinion.
IOW, you probably had done yourself a favor to not use the word "simply".
FWIW, I didn't like the word choice on not like an icon set with the word "hate", but well I guess that's what he felt.
Personally I do like the new icons. Keep up the good work!
Only pointing out that "simple" is something in the eye of the beholder. If you know how something works, it is often simple.
FWIW I have been working for over 20 years in OSS ;) and often thought things are simple only to find out that users need a bit more hand holding.