Many of the churches and cathedrals were built on hills and mountains in most big cities in France which makes them look more towering and impressive. Glad the area surrounding the church has greenery and it looks like an interesting one to explore.
Comparing Marseille to Lyon for example from the vantage point, there's definitely a lack of greenery and open spaces in this photo. 
I didn't imagine it to be so densely populated.
Yes definitely less green space than Lyon. We didn't see any city parks or anything. They might have had them but we didn't come across any and we walked a lot of the city. The harbor is more open but definitely very dense overall