A properly fitted corset is not painful, it's like getting a hug. Now, if you wanted to drop 8-10" from the waist...that takes "waist training", which is much more involved and time-consuming (think a year or two of 24/7 wearing)...but even that isn't "painful", it's like getting a "really big bear hug."
The relation between "pain" and "corset" comes from either history (corsets made 150 years ago weren't properly fitted
to the person, rather they were made to create a specific shape...ergo, pain), or from close association to the BDSM culture...in that case, the corset is a piece of erotica, not pain/punishment (that's what the candles and paddles are for

)
Anyway, glad I could help a tiny bit.