I have had an interest in New Testament hymns because I think our worship should reflect what we find in the New Testament. Also these hymns are possibly some of the earliest Christian traditions we have so they can give us important insights on the origins of Christianity. On these and many other issues New Testament scholar Matthew E. Gordley has written a very important book called New Testament Christological Hymns (IVP, 2018.)
Now on the possibility of these hymns predating the New Testament, Lindsay Kennedy writes in his review of the book,
For Gordley, the recent push-backs against identifying preexistent hymns in the NT are worthwhile but need nuance. Gordley argues that the hymnic classification of these texts should be detached from speculation about their origin. While it may be impossible to conclude any hymn is a pre-existing composition, the recognition that it is a hymn is still beneficial. For example, this identification allows one to interpret the text in light of other ancient hymns.