Pretty much the same idea but instead of a blast shield have some kind of AA system thst shoots down rockets. Then maybe have it so in order to take out the AA you have to do an almost impossible task. Or even have a boss that does an EMP that negates the use of synths so if there isn't any additional enemies other than boss you have to coordinate heavy ammo and use it carefully. Kind of like how in mmos you save you long/survival cooldowns for certain parts of a boss fight.