Amusing spin on things.
Not entirely sure why people find it complicated to understand the issue here.
What Manchester City have essentially done is claim that they don't believe the negative results because of the increase in number of positive tests, essentially that more players could be infected without the tests revealing it. You then ask the right questions about the risks involved and you get the obvious answer that yes, there is a risk that City's worries are real, that more players can be infected and then infect others, you then list the potential outcome and the Premier League can't really go against that.
The problem should be quite easy to understand. Every single time a club has an increase in positive test results, no matter if it's from 0-> 1->2 etc, that potential dilemma exists. There's nothing different between City's situation on monday than West Hams situation when Moyes&co got positive results, Sheffield, Arsenal, etc. As soon as you see an increase, the same argument can be drawn up and you can easily get medical advice to underline the risks involved.
Everyone knows that a negative test result doesn't mean that you aren't infected, every medical advice will say the same, but the only way things work at the moment is that the test results are interpreted as clear answers. You test negative you're negative and available to play, if you test positive then into isolation you go. If every club does the same as City when important players are infected, then the outcome should be fairly easy to predict.
City's concerns were so big that less than 48 hours after the match was postponded, the first team was back in full training. If the risk was really that big for uncontrolled spread of the virus within the club, the only outcome would've been to isolate the players for 10 days, you didn't.