Ayu is also much older now than Namie was then. That likely plays into the backlash, too. "Almost 40, two divorces, no children."
When it comes to Ayu's voice, I observed something. Reading the comments to an old performance on youtube (I don't remember which one) someone asked who made her sing from her throat, because that's bad for the throat. Someone said that if it wasn't for that high voice she wouldn't have been selling as much. So it's basically not about skill and technique, but about her tone.
I'm curious to know what would have been if she'd properly attended singing classes before her debut. We'll never know.
I was also suprised to see that Otsuka Ai's latest albums (I don't know about LOVE HONEY, though) didn't even make it into the top 20. So Ayu isn't doing all too bad for herself.