Even if illogical, given two otherwise equal cities, which is more "livable": the one with a stable and open atmosphere, or the one with scared citizens, under a state of emergency, where the country at large is implementing knee-jerk responses against the "others" who are related to this attack (referencing the current burkini bans rolling across France).
It would be much better if they directly measured the impact of this on cities though, particularly because the reaction to terrorist attacks is vastly different (see the difference in German and French reactions, for example). In fact, it could then penalize heavy-handed responses even when there hasn't been a terrorist attack. For example, the US maintains some draconian security measures and a police state mentality even though there haven't been any recent terror attacks (does every single MTA rider really need to be constantly reminded to watch suspicious packages?).
For that matter, I'm confident that you're quite safe from terrorism in Dubai. But the ranking should really include the dramatic security apparatus/environment which is in place to maintain that safety.
If you visit Paris now, you see more police, a slightly worse nightlife. Right after the attacks you could see everyone was really on edge.
On the other hand if you're taking into account this kind of mood/atmosphere, a place like Paris should be generally pretty low on that scale as people you interact with in your daily life seem a lot more stressed, tired, unhappy and sometimes aggressive than in any other French city. I know it's a stereotype, but it's kinda true.
The question is if the city's are worth living there assuming you can afford to.