If he starts again, how long is he going to play? It is a gamble to keep him because if he does not play next GW, or does not have enough game time, his value will drop, making it a loss to whoever is keeping him. I have him, but I am still deciding whether to keep him or not. Many people are not willing to make that gamble.
If he starts, he'll probably play 90 min or close to it. CB isn't a position you rotate after 50 minutes unless there is a problem.
4% of people currently have Quansah, I'd say that the chance of another drop in price is slim at this point.
Now it doesn't matter if he drops anymore. That first price drop is a problem since it means you can't pick any 4.5M defender for him now. You can only go for 4.0M and there isn't anyone good in that bracket. Of course, you have more options if you have money in the bank or if you are willing to use 2 or more transfers, but that is way too costly to remove the defender which was minutes risk from the beginning. If anyone still has him, I say keep him. The time to sell was before the price drop for another 4.5 like Robinson.
I am always surprised to see how many people are doing transfers after GW1. I mean we were all just making teams and nothing really surprising happened in GW1. I mean Arsenal and City kept a clean sheet, big surprise there, they are two best defenses in PL for years. Salah got points in an easy fixture, well that was also expected, if someone skipped on Salah or Haland it is because of price not because they are bad options. They aren't cheaper now. Trust in your initial analyses and let it stay for few GW unless something fundamentally changes.
For instance, I am not happy with Nkunku but not because he blanked in GW1. I am unhappy because he played less than 60 minutes and Chelsea now bought Felix as well. His minutes will probably be much worse than I anticipated and if that continues he has to go, preferably before the price drop but I am definitely giving him another chance.