People can't always shoot off a rest. Shooting off a rest doesn't tell you what you need to do to improve. Very rarely are sights even an issue. It's 99.9% operator error.
For me it helps tell me if my sights are off, or if I suck. I had an adjustable rear sight on my 1911 that would drift. I could never tell if it was me or the gun, the rest answered that question. You can use a rear sand bag those are pretty ubiquitous. I inherited a rest that has a cushioned clamp that is adjustable. I ended up getting some Novaks for the 1911 and it shoots more or less where I want. I can hit in the -0 on an IDPA target at 30' consistently.