When should we expect brittle program performance?

Back in 2015 a "Programming Language Performance Comparison"

http://www.hildstrom.com/projects/langcomp/index.html

On my old i5-3330 these times for unchanged programs —

    $ gcc -O3 -o test-c-gcc test.c
    $ time ./test-c-gcc 100
    real    1m36.599s

    $ time /opt/src/jdk-16/bin/java test 100 
    real    4m49.166s

Add one Java "final" keyword —

    $ time /opt/src/jdk-16/bin/java test 100
    real    4m49.166s

        final int array_length = 100000000;
    
    $ time /opt/src/jdk-16/bin/java test 100    
    real    2m58.618s

Or make array_length dependent on a runtime value —

        int array_length = 1000000 * iterations;

    $ gcc -O3 -o test-c-gcc test.c
    $ time ./test-c-gcc 100 
    real    4m48.034s

    $ time /opt/src/jdk-16/bin/java test 100
    real    4m49.567s

Should we expect measurements to be that brittle?