I agree with most of what you say but not this - it's entirely foreseeable that a certain proportion of an airline's fleet will be under maintenance at any given time. They should also anticipate that maintenance will sometimes overrun due to unexpected defects, shortages of parts, insufficient manpower etc.

Furthermore there'll be a number of aircraft each day that encounter faults or incidents as described above which ground them. With a small fleet you need to therefore allow a healthy amount of slack in the schedules for all of the above, or else have sufficient contingency plans to accommodate pax.

Unfortunately BA seem to plan their A380 schedules on the assumption of a best case scenario, ignoring the possibility or likelihood of any of the above occurring. That's a commercial decision for which they can, and should, be held accountable.