Sounds like a RAW software problem and not a lens problemIndeed. Try to do some pano with the RF 10-18 for instance (BTW, its vignette is worse at same focal lengths and apertures as the 11-22), and you'll see that most softwares are unable to work correctly with the raw files, ending in too many errors and artefacts that makes stitched results unusable, most of the time.The lens is for instance optically corrected.It still is.You also wrote "No equivalent anywhere else." That was maybe true in 2014, but is absolutely not the case today.You wrote itThe 11-22mm is a very good lens, but the almost mythical, legendary status...To my sense you nailed exactly what I call "the fundamental set of lenses for EOS-M". BTW, the 11-22 is really a gem, even in comparison to any other system to date.
. I only wrote it's a gem.
UWA lenses are also rather expensive for other mounts especially if you have to factor in the price of the camera body also.
Fortunately no manufacturer has exactly copied the 11-22mm because the locking/retracting mechanism is an absolute pain.The balance of size, weight, price, optical qualities and features of the 11-22 is still unparalleled in any brand by now.
It is no longer 2013. That review is comically outdated and some of the comparisons are just ridiculous. Who is cross shopping the EF-M 11-22mm against the Sony E 16-50 kit lens or Canon EF-S 15-85mm?This excellent page gives a list of its advantages against some other lenses at the time, but still, no recent lens can rival (even in Nikon Z mount line-up... so ).
https://www.witnesstobeauty.com/canon-11-22-is-review-and-comparison
Lens option have changed a lot in 12 years. Every current mirrorless system has wide angle options that are as good as, or better than, the 11-22mm. While the EF-M system has exactly one wide angle option, other systems have four, or more. If someone is already in the EF-M system, of course, the 11-22mm would be easy to recommend. For anyone not in the EF-M system, they will have their own excellent wide angle options. Many of those alternatives offer capabilities the 11-22mm can not match.