I don't want to dismiss cheating or other issues with going online. But when communication from IRCC has been as weak as it has, they are asking for people to make assumptions.
Pre-COVID, more than 80% of test takers were passing the citizenship test on their first try... it's not a particularly hard test. Unless there's data suggesting that a much larger percentage of test takers are passing the online test, I'm not sure what the concern is.
Regarding your school analogy, I have not heard any school say it will do online testing for only half its students due to COVID, or ask half its student body to miss a school year. They have been forced to make compromises, and iterate and get better. It's not clear to me why IRCC gets to decide it will process less applications. COVID has made life difficult for everybody, they need to deal with it.
I don't know what the right solution is... may be put big penalties on those found cheating? But the answer can't be delays for the vast majority of honest citizenship applicants.