The 2nd A380 at MAN will add about 60 outbound seats to over 10,500 on offer every day across MAN, LHR and BHX to the middle east. Plus the 1000s on offer non stop from LHR to destinations that avoid the need for a connecting flight from BHX or MAN at all.
Confused as to why anyone thinks it is a game changer
It's not a game changer in the context you suggest.
It is however significant in that, once travellers are aware of it, many choose to specifically fly on it. A trickle of just 40 passengers from BHX to MAN's A380s represents a loss of 10% of BHX's B77W capacity.