In any game equal opportunities for success or satisfaction for ALL players AT ANY GIVEN TIME is the key to any game..... whether it is a successful defence of a base or a successful capture.
A horde usually arises when 1 country has more numbers than the other 2, or is willing and able to weaken its defences on another front. Due to numbers fluctuations there is almost always the opportunity for a horde to exist in 1 of the 3 countries at any time.
And right now there is no defence against a horde, any horde from any country, when you are shot down by the first wave and your base is rendered unusable 10 seconds after the horde arrives. In the 5 minutes it takes to return to that base it has been captured.
Of course the underdog will become discouraged, and move on to a base where numbers are more equal or log off leaving the horde to continue its rampage. The longer the horde remains in existence the fewer options the underdog has. It is not conducive to the success of the game to allow these steamrolling hordes to exist for a lengthy period or its underdog players to become discouraged.
You want better fights, happier players, less whines? Give us better defensive tools so that the underdog players can break up these hordes or keep them occupied longer by allowing players to still take off from the base to defend the base's city: more acks, and longer range and more accurate acks, gvs that can hit moving targets, harder hangers, acks, ordinance.