Keep in mind that what looks poor asymptotics might actually not be, because you are working in a lazy language. In a strict language, appending to the end of a linked list in this way would always be O(n). In a lazy language, it’s O(n) only if you actually traverse to the end of the list,in which case you would have spent O(n) effort anyway. So in many cases, laziness saves you.
This isn’t a guarantee… for example, k appends followed by a traversal will still run in O(nk) where it could have been O(n+k). But it does change the picture somewhat. Thinking about performance of single operations in terms of their asymptotic complexity when the result is immediately forced doesn’t always give you the right answer in the end.