The problem with looking at online sentiment is that this is not a topic where the average person is educated enough on the subject to form an opinion that considers even a few of the factors that come into play when you need to find the right balance for something like an air vehicle. 
And this is where data helps us, combined with experience and logic driven by a cohesive design choice. For reference, I'm in the same skill bracket as my fellow pilots @SilkOCE and @HiebDE, and I've been flying air vehicles in multiplayer games for more than 15 years.
I'm a professional Data Engineer/Analyst in the manufacturing industry, so I'm a big promoter of data-driven decisions with enough context. Now I'll try to sum up some possible solutions to make everyone happy (impossible) without compromising the integrity and design of WARDOGS' core gameplay. Let's start by saying that I totally agree with the current sentiment of players that you should not see a pilot going 100+ kills every match (they're lying, but let's assume it's a fact or a high possibility), and having 10+ attack helis flying around at all times can be a terrible experience for infantry players. With this premise, we can start discussing what could be an optimal % for each role that leads to balanced matches.
With the current attack helicopter mechanics (miniguns, rockets, Havoc), I'd assume a good one would be 4-5% out of 100 players.
This value is highly influenced by the difference in skill required to be effective between the minigun and rocket heli (the Havoc is another bracket and I think it should be vaulted until reworked). Right now, the rocket version of the Little Bird is the most annoying to face for the average player on the ground, since it's basically just low-effort splash damage from the sky. And I think the current balance is tuned well enough for that helicopter.
You go in, dump some rockets, get a few low-effort kills fast, go out, resupply, repeat. Low risk, low reward: this should be very situational and the profit should come slowly. Totally fine with that. The minigun helicopter, on the other hand, is currently high risk, low reward: it gives the same profit ratio as the rocket heli, with 10x the skill required to be slightly effective with it. 
I don't want to go deep into numbers in a tweet, so here they are: Considering a fully kitted AH-6M with T2 armor, you invest around $18k upfront; to break even, you need around 13 kills, considering various other factors.
If you die, you can't get revived, so there are no second chances, etc. To keep the pick rate as low as 2-3% in an entire lobby, the mechanics and survivability need to stay HARD. But at the same time, you should give people more chances to break even, or to avoid sinking all their money while trying to learn a game mechanic. Considering the LIVE S2 build (BTK = bullets to kill): AH-6M (miniguns) •2 BTK on torso, no armor (FMJ) •3 BTK on torso, T1 armor •5 BTK on torso, T2 armor •7 BTK on torso, T3 armor •9 BTK on torso, T4 armor •Base kill reward from $1,500 to $1,200 •Introduce a kill multiplier that caps at $2,500 at a 15 killstreak •Buy cost from $12,000 to $10,000 •Base FMJ ammo in inventory from 300 to 600 •Diminishing returns after a 30 killstreak: back to $2,000 per base kill, no bonus from the HZ AH-6R (rockets) •Base kill reward from $1,500 to $1,200 •No killstreak multiplier •Buy cost from $18,800 to $20,000 •Base ammo in inventory from 6 to 12 rockets •APC destroyed from $10,000 to $12,000 •Tank destroyed from $10,000 to $7,500 •AA tank destroyed from $8,000 to $12,000 General •Flares from $750 to $250 This will help new pilots who test the vehicles, make no profit with them and still lose a lot of money, and it will let average pilots still lose money without going bankrupt after a few bad rounds.
Also, top pilots will make enough profit to play it consistently without needing invincible helicopters.