And like Memoria777, I rely on my naming scheme to deterministically find any playlist fast. For example,
1. I have a "_Commented" playlist so I can quickly find any video I commented in. This would at first seem not normally be impacted by moving to a date-based ordering, except sometimes I may add to other playlists so often without commenting that it moves away from the top.
2. I used what a programmer would call "locality of reference". I have playlists which would be about a general topic like "Comedy" but I have lists that are specifically about "Comedy - Stand Up", "Comedy - Hidden Camera", "Comedy - Acting", "Comedy - Other", etc. When I want to save a video, I don't think or remember the entire sub-list of comedy type playlists I have, I just move rapidly down to the 'C' (think it used to work by typing the letter too) and then a tiny scan later, I've plopped my video in its rightful place. Now with this new scheme from Google, I effectively have to do a full scan of ALL my playlists, which is time consuming, especially since the playlist name box is so small, to say the least.
You have definitely caused far more problems than you solved with this change so far.