I will answer orange bird on here as it has nothig to do with the other thread.
My opinion is based upon research, personal and professional experience. It is not fact, not is it superior, however is believe you would be hard pressed to find a behaviourist who would say that a multi cat household is stress free, because they are not. I have no doubt your cats are stressed in one way or another, not all stress is bad if they can relieve it, but they will be stressed all the same. Much stress is tolerated, and it is most likely that your cats tolerate the living situation best the can, and this maybe to a pretty high degree. But you would be amazed at the difference in cats when separated from siblings. Cats that have lived happily, with no obvious signs of stress, who when moved to single cat households becomes completey different cats. The slim line indivuals who suddenly become chunky monkeys, because finally they can eat food without pressure, the ones who were fat buggers slimming off because they don't have to grab and go, or because they have more outdoor access now, rahher than time sharing, the ones hat suddenly stop using the tray because they can access the outdoors to pee, the ones who's condition improves due to less obsessive grooming. Etc etc.
There are plenty of cats the live in groupings of 2-3 that thrive, but it is unheard of for all the cats in that group to be non-stressed, one will benefit from the relationship more than the other. Similarly a big groups of cats like yours will cope, but the will release the tension in other ways - if you say there are zero issues related to any stress then I do not believe you, cats are always stressed about something, be it food, sleep, other cats,building works, heat, cold etc - they can relieve this stress Ina. Variety of ways from displacement behaviours to scritting to internal health issues.
Don't believe me? Do the research yourself. Why would you not want to help relieve any stress by doing something as simple as putting a couple of extra trays out! If you are so confident there are no issues then why no do it anyway and prove your point.
I'd suggest really watching your cats, not as an owner but as an unbiast observer - look for a cat who starts washing whoever another cat comes in a room ( displacement behaviour) or one that won't look the others in the face, or one that's a little funnier than the rest, look at who eats when, who takes heir time, who doesn't. If they have outdoor access, monitor who goes out when, how long for, what for. Etc. you'd be surprised at what you will spot.
So no, to reiterate, not superior, I have oodles to learn, but I also don't arrogantly presume that my animals are perfect I had a thread on here not so long ago about my two boys scrapping like crazy, I was humble enough to admit I needed help with an issue I was to close to, I couldn't be objective.