I don't think anyone would say they've sold any of the mentioned brands based on SQ. Some may say they've noticed an improvment when moving from one brand to another, but I doubt it would be a factor before they moved away from one brand.
As mentioned, many people who move away from the mentioned subs probably do so to pursue DIY. Though it doesn't take a "ton of cash" to reach single digits, and it isn't only possible with ID subs. For the price of a JTR Cap you could easily build a DIY setup that outperforms every sub listed, hits single digits with ease and authority, all with better sound quality.