1) You say transporting mixed qualities is going to probably be necessary because you can't unsmelt plate, this is not correct conclusion. You can still make basic ammo and recycle them to increase the quality of iron plate, or do the same process with copper wire. No need to unsmelt plate whatsoever.
You also can't put quality modules in furnaces, and don't get quality items if you don't use quality modules. At this point your argument against inventory clutter even if true, i think is more to put on your inability to organize things /misunderstanding of the feature given what are your example of it.
2) It was said that liquid can't have quality and can't get recovered by recycler. What's even your point with liquid ? There are informations you don't have so the point isn't argumented it's just written there as a point that shows what ?
3) You are afraid people are going to misuse something ,therefore that thing should be changed but you have no proposition for it ? i mean in your reddit post, i don't think it make sense to apply quality just to module as a big part of what's good in quality is the bonus applied to the many entities, like larger radius power pole or robotport faster inserter , more powerful nuclear reactor, mining drill that deplete less the ressources. Which obviously wouldn't be there if quality was limited to module. Also no guarantee people won't misused your proposition and go for a all or nothing situation with module quaity, your proposition on the forum doesn't adress the point you make on reddit.
4) I have no idea why you think people would do what you think is a good solution. You don't expect people to come up with many different possiblities ? You think the feature is not good because you think of 1 way of using it that is not fun ? I don't think the point is valid ,i think you are just not seeing the whole picturs, and from limited informations you draw erroneous conclusions. As from the same pieces of informations there are many ideas that comes to my mind, that i find fun to try. Also at this point your point 4 is the opposite as your point 1, where you started saying "transporting mixed quality will probably be necessary", and your conclusion is " players will all only belt the max quality".
My proposal still addresses the T3 module issue, while also removing the clutter caused by qualities of normal items. Replacing modules with better ones is also way more convenient than rebuilding whole setups with better buildings.
The T3 module issue ? what's that ?
Replacing modules with better ones is also possible with quality feature you don't have to rebuild your whole setup if you don't want to but you could with the proposed quality feature, win-win, whereas your proposition is limited as compared to the current game it wouldn't add anything, sure you'd have several tier of module, that you can switch in your existing build, yay, that's the same as now.
Another good point about quality that you seem to have missed because your proposition doesn't adress it is when you have the currently maxed out setup in factorio; assembler tier 3 full productivity or speed module, surrounded by beacon. The quality feature introduce a new choice to the player, do you want to use the quality feature to upgrade the furnaces ? the modules in the furnaces ? the beacons ? the modules in the beacons ? or not use quality and duplicate more of what you already have. Maybe it makes a lot of options and it's difficult to predict what players will do but that also gives a lot of options to have fun, to try and fiddle with for the player. Whereas your proposition would be of very limited value in my eyes, as there would be no question, and only the quality of the module would be to upgrade since you removed most of the good stuff from the quality feature.
Currently a lot of people seem satisfied with the quality feature
A lot of people seem satisfied too though, and when reading the reasons why, many of the disatisfied people shows lack of understanding.
Edit; sorry if the tone feels abrupt, i took time to adress each point because i recognized the attempt making constructive critism, but unfortunatly i reading it again my answers doesn't show such appreciation.