Sevilla is a good team, they can prove it by maintaining his position in 2nd place on the table so far. They actually can compete with Real Madrid and they are doing it now. However, with the quality of their current squad, I am not really optimistic that they can overtake Real Madrid at the top table. Except Sevilla buys some top players in the next transfer window.
As a team, Sevilla has been winning consistently this season. Although there are also those who claim they play consistently poorly, it is less relevant when you're second in the standings. Sevilla should not blow the standing tables when they are in this situation, even if they are to be considered serious contenders. Especially when Real Madrid are at their best. Sevilla's title challenge has already passed the deadline.
The difference is not that significant. I would say that if Real keeps losing points, Sevilla has a chance. Sometimes you have to remember that it is not always about the "worse" team to win all the time, sometimes it is the better team that ends up losing. If Sevilla doesn't win all the remainder of the games that would not be shock to anyone, but if Real suddenly has a bad stretch of losses in a row then Sevilla could take the lead. So this is as much about Sevilla as it is about Real as well.
I say that there is a good chance Sevilla could keep this up, they do not have too many opponents this year, only Real that is at the top but nobody else, so all they have to focus on is playing very hard every single week for like a month or two and they could end up getting ahead of Real Madrid, after that they could lose points as much as Real does and still be ahead.