1) The Raspberry Pi 4 is THE cheapest 2Gflops/W computer ever made and probably that will ever be made in the future too! Peak of energy/resources/lithography/architectures and velocity of money against that, will most likely make it so.
2) You can scale the Raspberry cluster as you want it, only power the nodes you need, it's modular, one breaks you still have a few left, same for the SD cards which BTW while being so slow a Raspberry 2 (2W!) can saturate them they are SURPRISINGLY sturdy (my original SanDisc (every other brand has been a complete scam) are on their 7th year of 99.999% uptime, down when my power company cut the electricity for an hour).
3) The Raspberry cluster is smaller, cooler and silent (if passively cooled, it's the most powerful device that can be fully passively cooled at 100% CPU (7W) without becoming too hot to wear early) and wont fail because of failing fans!
4) For battery backup there is nothing better because beyond total of 100W for 24 hours you start to see the limits of what is practical to manage on a individual basis.
I post this picture every time: http://move.rupy.se/file/final_pi_2_4_hybrid.png (this is how you cool a Raspberry 2/4 hybrid cluster)