Yes, Quicksort’s ‘worst-case’ scenario is of O(n^2), when the algorithm is unlucky enough to chose a pivot that happens to be the largest or smallest item of the list. V8 tries avoiding this situation by finding a pivot as the median of the first, last and middle elements. You can also try choosing the pivot randomly to prevent a user from making your sort take a long time. Quicksort is a good example of very different worst-case/average-case performances, so I understand the importance of paying attention to this detail.
On the other hand, Merge sort’s worst-case/best-case/average-case is always O(nlogn) so you don’t really have to worry about initial order-set.
Hope that answered your question!