Actually a soil flush is not just for a dying plant.
I flush my mothers every time I take cuttings from them. They live in small pots and I fertilize them aggressively, so a flush is necessary every once in a while, and doing it at regular intervals prevents problems with salt buildup. It's good for them!
I promise it is safer to flush your plants than to let them sit in poor soil.
The problem I see is that your soil does not drain well. That makes flushing harder, but you still need to do it, test the runoff pH, adjust your flush water to bring it within 6.5-6.8 if it is out, and then do a final flush with some fertilizer solution.