Maybe explain what you define as "coin-flippy" ...50/50 chance of what exactly? drawing masquerade ball, playing masquerade ball. playing it twice or winning?
By coin-flippy I mean rng. It can be very strong but it also can be very weak. It's mostly about blue vs. red coin.
Double Ball is great at abusing red coin (being last to act). But if you roll blue coin, there are hardly any cards you can play proactively (generate full value without interacting with opponent). And people know to open with cheap cards or specials to force you to play for low value (like poisoning a 2 point unit or locking a unit that needs no lock or dropping Dames for an easy bullet) or for no value at all. That makes it hard to win R1. Lose R1 and you're losing last say in R3 so your opponent can develop his points in his last move, and there's nothing you can do about those points. And you're also gonna play first in R3 so the situation from R1 can repeat itself. Double Balls are quite weak on blue coin. Also, you often struggle to get that round control and you empty your magazine too early.
Second, Ball engines (Dames) go down with 4 or 5 points (5 when played to scenario), no armor, no boosts. So they are very easy to cheaply remove. If your opponent happens to have drawn his removal, he's getting a lot of value out of killing those Dames (kills a unit with like 9 point potential by using a 4-5 provision card). While this is true for many engines (like Dryads), Ball is different because it can hardly develop any value on their side without them. So it very often comes down to if they drew their Joust/Stunning Blow/Boiling Oil, etc. And when they did, they put nothing new on the board so the situation described above repeats itself.
Third, NG seems to have a card for every situation. Yeah. But if you gotta draw those cards when those exact situations arise. If fail to deny value exactly when you need to, and there is a big chance you'll lose. This is true about every pure control deck. It's very rng.
Last, Ball is often auto-lose against point slams like elves or NR. All those high provision cards like Yen or Vincent lose value when there is nothing good to kill/steal.
Do you have a higher % win rate against NG (using another faction)? what's your win rate against them, above 60%?
Where I am right now I mostly lose lol. But I don't lose to NG any more than to other things. Depends on the deck. I lose with SK. But I win with NR and ST. I don't play MO and SY so I don't know but MO usually loses to NG and SY is more or less 50/50 afaik. Also depends what exactly you play from those factions. Greed decks going tall are usually auto-lose against NG, sadly.
A tip against NG: get another strategem. Tactical Advantage sucks against NG. You're basically moving 5 points to a unit that's gonna die anyway, and you deny yourself the only little advantage you have on their red coin. Magic Lamp or the ST Sabre is great.