Helicopters before TOW were worthless. After TOW, they got value.
Helicopters are a tool that, at the right time, can be provide great value.
Here are some instances of the value provided by helicopters, that no other unit can provide:
-The Re-base Airlift. This is done by loading units unto a helicopter, and using the rebase option. This is a great way to reinforce or provide offensive units to cities faster then ships.
-Airdrop Looping: Because helicopters return to their home base, they can be used to send massive loads of troops to another land mass. Helicopters can carry 3 units 8 squares in a single turn. They then return to the home base, ready for a new set of units, which can be delivered to a different location.
-Can move the TOW Inf.: (If you can tell, I'm a big fan of these units. TOW can give a big bang, both offensively and defensively. They are cheap to produce. And also importantly- I've seen them time, after time defeat tanks. Never count them out of a fight.) This gives a player, an extremely mobile and powerful option.
-Afghanistan War Strategy: The US strategy in Afghanistan was to attack using special forces and Air power to defeat a weaker nation. In Civ, you can now use airpower to soften up a target and let TOWs finish it up. Once a city is captured, helos can rebase in the city for further reinforcements.
Despite all I said, Helicopters are still underdeveloped in Civ. Here are someways for them to be improved:
-Allow helicopters (and units they can carry) to work off of Aircraft Carriers. Part of the reason helicopters can't be used is because land masses are rarely in the right place to work optimally. Allowing them to work off carriers would allow their worth to increase exponentially.
-Allows them to do other missions that increase their use. Anti-submarine patrols are a great use for helicopters (as El Justo).
-Allow Helicopters to do extractions, which I was wondered for years was not implemented. There have been numerous times where I have not used helicopter or paratroopers cause it was too much of a hassle to get them out.
-Allow helicopters to carry more units, but NOT armor. What I'm thinking of is like artillery, not RADAR Artillery. This would allow helos to back up the foot units with artillery defenses. To keep game play balanced, helos should never be able to carry Armor. (In addition, this is rarely done in real life. Note that the tank in the picture was a small one, not a main battle tank.)