If we strip whitespaces in the merge sort version you provided and apply same formatting it becomes a 30-liner https://pastebin.com/KmWBMC0M vs 31 lines of PHP.

You can’t beat that kind of productivity.

How do you measure productivity and how can you prove that productivity in PHP is higher than in C#? In my career language was never a productivity bottleneck. Good quality frameworks and libraries do make a big difference on the other hand.

That’s an excellent question, but they were just quoting the article.