Fortunately, MAN only requires growth of 1.5% - 2% to achieve the 23M target by year-end. That sounds 'doable' but we must remain mindful of the setbacks to be overcome.
Shed, you rightly draw attention to the negative impact of security issues and the threat of terrorism in certain countries, and flight cancellations due strikes, which can have a knock-on effect on confidence. Strikes in the past have often been associated with France or Italy but the Lufthansa issues have now been ongoing for some time.
However, given that the ACL winter report for MAN showed an increase in seats of 9.7%, there would seem to be a reasonable amount of room for such offsets and still achieve 23m, unless load factors take a dive.
On diversions, I'm sure I read a while ago that pax are attributed to the intended destination airport and not to the airport where the flight diverted. If true, I'm not sure whether it only applies to 'splash and dash' diversions or to pax unload diversions as well.
Edit: I see eye2eye5 has now made the point. Can you clarify if it applies to all diversions, irrespective of whether pax are dispersed at the alternate.