Well the idea is that they are good enough, but have been cheated out of it by a team not playing by the rules. In any case, they'd be better than probably half of the other teams in the tournament, so why not?
Personally, I don't actually care about the FFP thing. Like Al Capone getting busted for tax fraud, I'm just glad something is being done. Once you acknowledge how vile the City project is, why does it matter whether they managed to funnel blood money into the club legally or not? And at that point also, I think the manager, players, etc. have to shoulder some responsibility? Did they know their employer was flouting UEFA's laws? Maybe not. Did they know their employer was using the club and them personally for something beyond reprehensible (and still are)? Yes