I'd suggest describing it as a "colourful alternative" rather than a "modern replacement", because no-one will be removing /bin/ls with exa installed. "Replacement" strongly implies removal of the thing being replaced, as with "replacement hip", "replacement CEO" etc.

As for why anyone might feel aggrieved about replacement of core Unix services, my mind immediately drew a (possibly unfair, but emotionally comparable) parallel with systemd.