Certainly an arranger keyboard will never (I never like to say "never", lol) will replace a band's work, and the sound quality won't be the same as real instruments being played by real people.
But I can say with certainty that with my PSR I do a better job than many bands in my region and I go further, I do the work of many different types of bands (rock, samba, pop, forró, country, dance, acoustic) which it would be almost impossible for just one band to be able to play all these styles.
My keyboard is not only a band, but an entire orchestra.
And yes, a well-rehearsed song, often with the help of regional samples, can compete with several bands and depending on, do an even better job.
My 2 cents contribution (lol)
Enildo