I don't think anyone thinks the assets bought in QE were worth $0. The Fed's impact was entirely at the margin (increasing the supply of investable dollars).

If the assets bought under QE were sold for 50 cents on the dollar (for example), even the most bearish investors would be lining up to buy in droves. Of course, that applies to investors with actual money behind their beliefs rather than random internet commentators who can pull valuations out of nowhere.