Honestly, labour's problem isn't that they're copying reform on immigration, it's that they aren't doing anything left wing like funding the NHS, or restoring social safety nets. If all they are doing is being reform light, then reform voters will inevitably prefer "full fat" reform. What they lack entirely is a unique selling point.
The article almost gets it when it talks about reform attracting "collectivist-minded group who are nostalgic for well-funded social democracy", but never follows that to it's logical conclusion. Those people perceive that there is no party that will restore that funding, so they embrace a party that they believe will protect it's decaying cadaver.
I once read a study that said left wing socially conservative voters were the most under represented in most western democracies, and the current situation demonstrates the danger of that. If there is no left wing option that isn't perceived as extremely liberal, they will end up in the hands of those who style themselves as socially conservative.