But prolonging the inevitable is still useful, in that it slows down the number of hospitalizations on your march towards the inevitable.
Most hospital systems in the USA are stressed to severe levels. We had a nursing shortage before COVID19 even began, and the increased workload from COVID19 is clearly causing problems.
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Slowing things down gives more time for the old patients to leave the hospital, meaning doctors/nurses won't have to work as hard.
There's going to be a negative correlation between severity and something like "velocity" of infected persons.
If a virus that would make make you very sick is contracted by someone who's vaccinated - They will now be in the 2nd category you describe ~'Sick, but not sick enough to stop them going out' -- They're now giving mobility to that virus that it would have otherwise not had (If they weren't vaccinated and were feeling too sick to go out and about)
So by usage of vaccines that only prevent severe symptoms, we pervert that normal negative feedback loop of virus spread and instead set the parameters to be more likely to propagate severe virus' that would usually keep you sick at home.
No, not _all_ transmission. Neither _all_ symptoms.
And then it goes on because measures are reduced, and zero-covid never was a goal... would even go so far that some few countries pretty successfully did zero-covid strategies and stopped their virus, though sure, that is a pretty futile thing if the world is not "globally" doing this and you are likely not isolating forever/completely - so we just start to live with it.
Statstically speaking, almost surely yes: with millions of infections there are thousands of variants, every day. If somebody was prevented from infecting somebody with their variant (as patient 0) technically we stopped variants with lockdown. Maybe they more favorable for us, maybe they were more dangerous from us.