I'm fine with growls in Epica, and it looks like someone else is doing growls with him, based on what I can hear.
Mark is just not a great growler. He's getting better, but he's still a pretty mediocre growler. Beyond that, the growling is usually extremely redundant. If you look at the "rhythms" or whatever he is growling, they are often super similar to each other.
I think if they layered the growls a bit more and really varied up his delivery and how he writes, it would be better. Then again, variety in general would really help Epica.