I guess it is hard to do a search on this particular topic, but a thread like this comes up about every month or so on the site.
Yes, you are missing a number of things.
First, the options/features you describe, like dual mono operation, are totally unimportant to many players. So, don't assume the benefits that you think are important are important to everyone.
Secondly, for those of us who play at a professional level, and/or in the pop, jazz, or funk world, it is a rare (if any) gig that can't be handled by a 410/212/115 sized cab (or even a 112 or 210 in many cased). Put another way, for many players like myself, I never, ever have to be louder than an unmic'd drummer. So, that 400-600 watt power range into a moderate size cab with good efficiency handles every gig I need. So, again, zero advantage to more power.
Thirdly, combine that with the difference schlep's we all have (in my case, I play mostly on the road in large cities, and often walk blocks to the venue from my car), as long as I don't compromise my tone, the smaller the better!
Your comment on reliability is not supported in fact. Yes, some amp companies seem to have high failure rates, but if you look at a company like GK, there are just as many problem posts on their 'non class D' amps as there are on their class D amps. Don't confuse amplifier topology with brand or production/design quality.
So, if you don't 'listen with your eyes', you will find, like many of us who kind of make a hobby out of checking out gear, that there is virtually no measurable differences among different amp topologies (except, I guess, all tube amps, which are kind of a different thing when pushed to overdrive). Put another way, if you 'blind tested' 10 non SMPS amps (that is really what makes a small amp small and light) with 10 different SMPS amps (class D or not), no one could IMO and IME reliably identify the topology above the range of chance. All 20 amps will sound different, of course, and you would dig some and not others. However, it would not be defined clearly by the two power topology groups.
That being said, if you play really loud, and for some reason feel you need multiple 4ohm cabinets or whatever, a PA amp and preamp is a valid option. Of course, using your logic, I am sure there is someone out there that would say 'why not use a CA9.... it's the same size, and what's another 40 pounds
There is a reason that 'heavy PA amps' have virtually disappeared, even from high end concert level sound companies.... there is not advantage to the weight regarding performance
