This is just my experience and opinion therefore it is free.
I have a milled Brownells slide and several Dueck Defense dovetail mounts with built in back up sights. I don't even have sights on the Brownells because, with my older eyes, iron sights are nothing but a blur now. I find the back up sights on the Dueck to be merely a nice to have formality at this point.
Adapting to a pistol mounted red dot takes training/practice, but I have not found it to be nearly as cumbersome as some people describe. I don't see any difference in my milled slide versus the Dueck Defense mount in speed and target acquisition. But even if there is a slight difference, the benefits of the RMR, in general, are worth it to me at this stage in my life.
The Dueck Defense mount is easy to install and costs a whole heck of a lot less than custom milling for sure.
I think you need to keep in mind that things happen fast in this industry and change is constant. We have witnessed the greatest advancement of modern martial arts in history since 911 and the GWOT.