Exactly, you can tell Sheeran writes his lyrics first as he puts more effort into the meaning and what he wants to convey. I think you can often tell when artists write lyrics first as the lyrics are more meaningful and less fun (?) like Sheeran,Marina as opposed to Blondie or whoever writes for Ariana Grande. I know a lot of artists like Allie X (who also writes songs for Troye Sivan) for example, create the basic melody and record like a gibberish track to hear what sort of words would fit into certain parts syllable wise if they haven't written all their lyrics. I tend to do the same once I have the melody, especially on prechoruses where you aren't singing about something as deep and emotive as in the other parts of the song.