Barcelona in laliga is far better than Sevilla and if Manchester United was able to handle Barcelona in europa league that means Sevilla that has been struggling with their performance won't be tough Manchester United to defeat. I don't see Sevilla tough based on their performance this season.
The performance comparison between Barcelona and Sevilla this season in La Liga is clearly very different and yes, Manchester United will not feel overwhelmed in facing Sevilla in this Quarter-Final round. Because Manchester United also looks tougher when playing at home so the chances of getting a win at home to Sevilla are much bigger for Manchester United although they also have to take this opponent more seriously in this round.