I think there is more than one creature at work here. I've seen the one species with, one barely affected tanks. I had white cysts on a T heteromorpha group for close to a year, with no tankmates affected. It looked like Ich, but it clearly wasn't, whatever it was. Meds did nothing, but it did nothing either.
I 've also seen heavy death rates in well run tanks. It's a parasite that exacts a price if it isn't promptly dealt with. You deal with it effectively.
In my own set up, I see ich as annoying. I don't expect deaths , and am very surprised if I can't clear it up with the regular meds on the first cycle. I don't play around using heat, because there, there are credible reports of a form that tolerates the old 85f quite well. To me, I whack it with a med, and it dies while the fish thrive. But like you, I've been at this for a while and have developed skills. People who need to post for help tend to have new set ups and those add to the stress. I would not advise them to let it run.
I think that as it runs wild in a tank, repeated attacks affect even the healthiest fish. Again, we'll hammer it when it pops up. But if aquarists get into herbal treatments, heat alone, salt or even garlic to fight it, it has a pretty good time getting its meals in. That's not to say some of those treatments won't kill it, but they aren't the quickest. I prefer to wallop it fast, and move on to better things.
I wouldn't equate it with a cold. It's more serious if neglected. It doesn't go away on its own, and it wears healthy fish down if it does gain purchase. I find it doesn't usually do terrible harm to large fish, but it can wreck small ones. It obliterates fry tanks. Cyst size to fish size probably explains that.
A support for your view is that here, in Canada, it's a winter parasite. I don't think I have ever had an outbreak in fish bought in warm weather. But if fish get chilled in transit (a solid stress) they are very open to attack. Around here, winter is when people stay home and get fish for their tanks.
That said, I am now mainly a killifish keeper. In 30 years of keeping Aphyosemion, Epiplatys and Fundulopanchax, I have never seen one one cyst on any of them. That tells me either the parasite can't get to them as a group, or they have defences if it does tryo to latch on.