The disadvantage of bitcoin is its transaction time. We are paying for a huge transaction fee now but the transaction time keeps on increasing. I know that lightning network is not a thing and probably not going to be a thing in the next couple of years but this doesn't change the fact that both the transaction time and fee of bitcoin is its disadvantage. It's still cheap compared to other ways of sending money, though. As day goes by, this disadvantage keeps on getting worse and worse.
Another disadvantage is the community where everyone is trying to pull each other down. I think it is limiting our growth since we do grow by supporting each other and not by competition. We should help each other instead of spreading FUD or promoting things for the benefits of no one but ourselves.