A couple of people have posted this recently, but my experience seems to suggest otherwise (not saying you are incorrect, just wondering why my experience is different).

Over this past Christmas, I was on an F award ticket, and there was a flight cancellation. Upon rebooking via the app, I chose itineraries with First saying confirmed, only to find out I was put on the standby list for a seat. In both cases, people were cleared off the upgrade list into F before standbys were cleared. So in December I went from having a seat in F to a middle seat; they cleared the C+ upgrade list too, then cleared standbys. Looking at the lists in the app, I'm in 15E with cabin listed as "First" while someone in Main 2 is sitting in 15D, 17C, etc. The flight was coast to coast, so sort of a big deal; not just a short flight...

Then in January, I was on a flight with an RUC cleared at booking, and T-9 hours my flight was canceled. Again, rebooked via app and was lucky enough to get a seat in F immediately on the longer flight (it was a Saturday morning flight and I jumped on the app immediately, so that probably helped) but was put on the standby list for the short connecting flight to ATL. Again, upgrade list cleared before standbys cleared.

My experience with IRROPS is that I'm always put on standby, even when I see "confirmed" in the app when I rebook, but given a seat request card. Seat request is understandable since it is within 24 hours, but why am I not put on the upgrade list? I seem to be treated like a true standby passenger, but #1 on the standby list due to IRROPS and Diamond. I wrote a complaint in December and they gave me a $100 eCredit. I asked about downgrade compensation and they never wrote back again. Didn't even bother sending in a complaint for the second one since it was only an hour flight and not worth the hassle.