From what I think about uour covers there sees to be something off. On your first video that you posted, you sounded slightly out of key; when it comes to the overall sound of your voice you have a nice understanding on how high and low you sing. Justvthe thing that irks me most is that the vocals seem to not fit the instrumental. They both seem like two separate audio tracks that merged together in an uncanny way. This isn't just you though since I see it happen with a lot of fandom covers. Personally, I think the overall mix of the covers need work since they sound muddy to me.
If you need me to explain anymore points on what I said; feel free to ask me to elaborate.