The two are in no way equivalent. Disabling the journal does exactly that: turns journaling off. Setting the journal mode to writeback, on the other hand, turns off certain guarantees about file data while assuring metadata consistency through journaling.
The data=writeback option in
man(8) mount says:
Data ordering is not preserved - data may be written into the main
filesystem after its metadata has been committed to the journal. This is
rumoured to be the highest- throughput option. It guarantees internal
filesystem integrity, however it can allow old data to appear in files
after a crash and journal recovery.
Setting data=writeback may make sense in some circumstances when throughput is more important than file contents. Journaling only the metadata is a compromise that many filesystems make, but don't disable the journal entirely unless you have a very good reason.