If a mediocre team against a top team only gets small odds, but of course you can still get big odds with other options. But indeed, to get big odds in a match between a mediocre team against a top team will have a high risk too.
But I think it's relative because not all bettors will look for high odds in just one match, because usually they are also looking for high odds with multi bets. In fact, in this match between Chelsea v Arsenal, I'm sure not all bettors will bet on ML, because they can play it safe with the option of draw no bet or double chance.

But regardless of which option you choose, the match between Chelsea v Arsenal is indeed a very interesting derby at this moment because Arsenal are usually under Chelsea but currently Arsenal are even still at the top of the English Premier League standings.
This factor is certainly very interesting because Chelsea and Arsenal got very different final results in the previous match, where Chelsea lost big and Arsenal won big. It will at least have an impact on their performance at this moment and therefore, I also chose Arsenal to win but maybe I predict Chelsea will find it difficult to score until the match does not have many goals scored.