How is it a fallacy? If Morgana is popular people play her more, she sees more games, people will try to supplement her weakness and thus the knowledge of playing her will more easily accessible. Thus people will do well with her because many people try to master her, when a counter comes along and wrecks her, people will move to that one and then supplement that champions weaknesses, who will then be destoryed by another counter and so and so forth.
Its a logical system where things that where considered weak and now strong, simply because of probability of what it will play against. Its pretty much like starcraft. Someone masses zerglings, you mass marines, they mass rouchs, you mass marauders ect. But its predicting what they choose. Not 'who is currently strongest.'
Remember when AD casters assassins were going mid? Then items got nerfed and people found counters and then people either tried to fix the holes or like most people moved on. If Morgana proves to be so popular and such a 'go-to' pick then she will most likely get nerfed just like every other champion.
Also take into account that this is "support Morgana" we are talking about and not "AP mid Morgana". Those stats prove nothing more than she is picked a lot and it surely doesn't say anything about her position, and while she appears good in platinum she is hardly played in platinum, in diomond she has a half win rate. With gold only being slightly higher in win rate. She is also shown as being hardly picked.
If anything this proves that she is unpopular and only choosen under certain conditions.Ā
And yes I did read the stats, I always used the stats to make my own point. Which is backed up by the same thing you claim helps your arugment.
Thus, because she isn't choosen we can say she is obviously not built for our current meta. Which still proves my point either way. It is highly unlikely that support Morgana got those win-rates when much more useful builds exist.