Both Real Madrid and Arsenal are doing well in their domestic league, and that shows that both teams are in great form, and if it comes like that, I don't think Arsenal have anything to be afraid of meeting Real Madrid currently. If the Arsenal squad should be afraid of meeting Real Madrid, I also expect Real Madrid to be afraid to meet Arsenal at this point. And as for the match against Sevilla and Arsenal, it will be a tough match because currently Sevilla is back in form and they are performing well recently, and Arsenal is also doing well, but if I am asked who has the best chances to win the game, I will choose Arsenal because I view Arsenal as a better team than Soliva.
It's very important you understand that Real Madrid have got More experience with the champions league than Arsenal, real Madrid is always having an appearance more often in the UCL than arsenal does , so their vast experience would be a very big advantage for them as the know how well to handle big and small teams at the UCL, having played UCL to finals severally.
Using the performance of arsenal in their domestic league to be a yardstick of comparison for both team may not be totally correct and out of line at some point, Arsenal has not really have the very awesome performance at the UCL but has done such with their domestic league but Real Madrid has done well I'm both, showing they have the dept of experience and capabilities to fave arsenal and win them if they happen to meet after the group stage.