I hate that ranged is the only real way to go.... because melee is useless 90% of the time "Weakness physical, flying" FUAAA!! xD i suggest grabbing a ranged of every element and pumping points into hero's ranged skills. if you want to progress.
Time consuming? Yes, Hard? no.
If you want hard go play creeperworld evermore.
The differance being that if you dont finish the level in 60 minutes (or 30 i dont honestly remember) you trigger survival mode.... aka all your work over the last 60 minutes gets flooded. Now this can be avoided if you build like 1,000,000 speed and reactor circuts but you arent likely to finish the level that way.
 "Protector IV.V"){kind=icon}
 "Creeper World 2: Academy"){kind=icon}