It's possible to make Rails relatively fast.

But Ruby is one of the slowest languages around. And Rails adds a lot of runtime overhead to that. It really is very slow out of the box.

And that matters for virtually no-one¹, because almost no-one is running their rails app at that scale.

That something would outperform Spring is really due to technical choices, the stack, suboptimal use or libraries. Because Java is undeniably multitudes faster than Rails; in everything.

¹ This used to be my strongly held opinion. But I'm shifting around since we're in a the middle of an unprecedented energy/climate crisis and a slow rails app is gobbling up electricity much more than a highly tuned one. Or the same service rewritten in Go or Rust or Java will.