Yes, late game and team fights are another matter, and it will depend on your team composition which one is optimal. Leona is good at initiating, which is often relegated to the support role in the current meta, so it is definitely a solid pick. If you need peel for a high priority target, Lulu will perform better than Leona.
I was talking mainly about the laning phase, as that was what the discussion before was about.
I was talking mainly about the laning phase, as that was what the discussion before was about.