Given the cash EI have in the bank, the LHR slots, the assets (they normally own roughly 50% of their fleet right?) and the fact they are a profitable business, I think this was deliberate undervaluation by IAG, they put in a bid they knew would get rejected to put a shot across someone's bow. Either giving the shareholders a heads up that they're interested, or warning a rival that IAG may start a bidding war and make things very expensive.
If you wish to claim that with the aircraft and slots then EI is worth a lot more then lets see............ sell the slots and see what EI is worth.
Not really a lot as second hand aircraft are still second hand aircraft and then EI has all its debts that need paying, the redundancy program that follows and eventually after all that you will end up pretty close to the value put on it by IAG.