> However, there's a tendency to undervalue PHP-based applications

I don't think there's that. In every thread about PHP, many people come in to explain this (edit: this = how good PHP is for use-case X, or how good it is holding up). Every time.

"We" all know PHP has its very well-fitting sweet spot. Its use-cases where it shines.

I do think, though, that the list of use-cases and the size of the sweet spot is not as big as the usage of PHP makes it out to be. What I mean is: there are many situations in which PHP is the best solution. But in many places where PHP is employed, it is not the best solution (anymore).