UPS's, at least those at the home/smb level ($100 to $250?), put out good power (most designs), but they also cause THD on the house wiring. Perhaps the 1st consideration is "do I need to keep this thing running, and as a bonus, give it good power while protecting it 24x7"?
"Distortion can happen in any electrical system regardless of how the power is supplied to the system" ... and ... "grids at 99% of the time, and inverter-gen at 1% of the time" might be supplying good quality power, but they can't "clean up" distortion (THD) caused by everything else in your home. So, does the (expensive) device need protection from everything around it?
A UPS that is "always on" 24x7 might become necessary/wise for a $10k device (your hvac, $4k fridge, etc.), even if the UPS adds to that distortion level for other devices sharing the home's electrical wiring.
And another consideration might be, does the expensive thing have a good quality AND external/replaceable SMPS power block in front of it? These eat bad power all day long, and only present good power to the expensive device behind it. These may not need a UPS, unless your other requirement is "it must always be on".
Whereas, if the expensive device DOES NOT have an external SMPS power block, easily replaceable, then it might warrant the UPS, just because it's internal power board is weak in design (hvac?) or more costly to repair/replace. This thing may need a UPS, even if the owner's manual or the installer doesn't tell you it does.
I don't have or see the "correct" answer(s) ... just more mud for the water, but there's some trade-offs to be sorted through.
Agree that this topic is akin to a can of worms and it doesn't help when we overanalyze it.
But just to put my point across, a UPS for a central HVAC would likely need its own room, wouldn't you say?
It seems for years, prior to some of our "newer" technology we ran with "generators" powering our homes for periods of time, and seldom did an individual encounter an issue.
Then technology improved? Or did it..suddenly we are worried about potential issues. OK, fair enough, but the question I have is just how "necessary" is an invertor generator for "back up power" when the intent is to "maintain" heat/light and cooling"?
Just as size of units is a variable, what does one truly need?
Cell phone charger..you can use your car, no UPS or invertor there.
Lights, again, lets be honest..how much do you need?
Freezer and fridge..are they impacted?
Heating and cooling..these units survive rolling blackouts and such
Now that big screen 58 inch tv..is it essential?
Computer? No power, most likely no WIFI or internet...
Until two years ago, I never owned an invertor generator, and from 2013 on I have had a generator for camping, both my travel trailer and camper. and yes, I boon dock...lots of "forestry" non serviced sites in my area..also use battery and solar.
So, the question, for those of us who just want the basics..light, heat and water..is an invertor necessary?
Technology
did improve. More than anything, the improvement came in terms of added capabilities and efficiency. I've lived long enough to remember the 70's and 80's where wall warts used to be a small transformer with a rectifier, basic ripple filter, and mostly on exotic ones, a linear voltage regulator. These were bulky, heavy, makes a tad bit of heat and don't produce as much current for their size. They're inefficient as well, citing information from the web, they're only approx. 60% efficient.
Those have all been replaced with SMPS for their smaller footprint, lighter weight, larger current capability, and high efficiency (80-90%).
But improvements didn't stop there. SMPS in the last couple of decades, give or take, have been designed to also have power factor correction (PFC) built in. In a nutshell, this reduced the harmonics it emits back to the AC line by nature of its poor power factor from the switching circuit. The downside is, owing to these design changes especially with active PFCs, they also became more susceptible to or affected by harmonics from a high THD AC line. This is what makes them vulnerable... aside from voltage spikes, transients, etc.
As to your last question... well, it depends. Are you a betting man?
Go for an inverter generator if:
1. You can afford one in the size that you need
2. You run critical (ie. medical, emergency) devices that needs to work, whatsoever
3. You plan to use it for camping and to be as quiet as possible
4. You want something that is fuel-efficient
Go for a conventional generator if:
1. You're on a really tight budget
2. You need 12kW or higher
3. You have no issues with noise levels
4. Outages are relatively short and/or you're not worried about fuel consumption
My stand remains that it is unlikely that a conventional generator may cause actual damage. But it's not to say that it won't. In the end, it's really up to you how important your electronics are and if you're willing to take that chance.