I have researched the ghost follower thing and decided to use my time for better things: targeting the right audience, choosing the right hashtags, and delivering great content.
As I have 14k+ followers, this would be too much work. And IG will know that accounts, after several years, accumulate inactive accounts who followed you and then stopped going on to IG or started a new account.
The worry of many is that IG shows your post first to a group of your followers.If they don't reply, then your post sinks.
I think this worry is unfounded. IG usually shows your post to those you have been in contact with. So it's unlikely that it pulls a test sample of people who haven't logged in for a long time. More likely, the test sample will be pulled from those accounts who are likely to be right for it.
Also, IG tries to punish for cheating. But amassing some defunct followers is part of the game and unavoidable.
I think it is more important to develop the active part of your audience than to remove the inactive one.
I can't do everything, so for now the ghost followers are allowed to haunt.