yes but it depends how determined the attacker is, yes they could go by sea, but wouldn't a para assault make more sense?
As for the air defences, you could think more WW2 big wing tactics, and the limited number of defenders are to overcome, afterall they carry a finite amount of weapons, and can only be in one place at a time. If you have 8 AA missiles and 16 attackers? Yes you would be sacrificing aircraft, but with the potential for several billion $ in oil revenue, the costs are fairly low.
Likewise we know that the odds favour the defender on the ground, but if they have neutralised the airborne defence, then they are free to shuttle more paras as required. How many sorties can they fly in a 24 hour period? Could they deploy sufficient SAMs to prevent us from flying in reinforcements, without taking the airfield? Then it becomes a siege mentality.
As ever it depends how desperate the enemy is, and what is at stake.