I suppose that all depends on your water. I tryed for 6months with out my RO and my garden went to shit. I had to fight many a lock outs that ive never had to deal within my system. My straight tap water was also knocking nutes out of solution. Had to clean my tank every 3 days from salt build ups and all my run off treys became super sparkly with mineral built up. I now only need to clean at the end of the run with a simple wipe out and no scrubbing encrusted minerals.
Since I've reinstall my RO not a sign issue. No lock outs, no ph issues, I'm back on cruise control with lovely healthy plants. It's a night and day difference in my garden.
I don't denie your statement but I do believe it's very situational to the water hardness of where you live and how you grow.
I would never get rid of my RO machine.