Compare Symfony2 with Spring, for example (~500 vs. ~22'000 responses per second).
Or if you want to only use the raw language itself, php-raw with ulib-postgres (~90'000 vs. ~300'000 responses per second)
And with PHP, the larger the codebase, the slower it always responds, because even with opcaches loading it into RAM is a major bottleneck.
That’s exactly the issue at hand here.
And compare actual performance, for example JSON serialization, that’s not even fair anymore, symfony2 reaches around ~2'000 a second, gemini, the fastest fullstack framework, reaches ~970'000 a second.
Raw PHP reaches still ~170'000, but the fastest non-PHP raw language is still at ~2'200'000 compared to that.
These are actual performance issues that will cost you actual money. Even saving 20% of hardware and server costs can be the difference between your company being cost-effective and dead.
A rewrite I worked on, from PHP to C++, had an improvement of 20 times better performance.
That's only one (1) order of magnitude.