There are some instances of what the OP talks about but there are far more of the opposite.
The Transfer Forum is rife with posters who make out anyone we’re remotely interested in is all of a sudden world class and any alternative views to them being world class are shot down. Loads of people start getting protective over these players like they’re related to them.
I posted every game I’ve watched Jude Bellingham where he’s been anything between average, anonymous and shite against a fairly long list of teams with good midfields and it was told I was being selective. When I asked for examples of where he’s had a great game against anyone at that level, nobody could provide an example, which doesn’t remotely suggest he’s worth the £125m some were saying City should have paid for him on his thread.
Even when it came out that Bellingham and his Dad said they weren’t interested in City because we’re a ‘plastic club’, people were still defending him like he was their own son.
We’ve also seen it when we’ve been interested in the likes of Pogba, Maguire, Sanchez, Jorginho… one minute they're the best thing since sliced bread, they’re going to slot straight into our staring line-up and Pep is going to work wonders with them; then when they sign for United or someone else, it’s radio silence. Years later we see how shite they were for the clubs they signed for a we got away with it by them not choosing us.
Some were even like that with Johnny Evans (although that thread had more the other way).