I am going to add a bit more context as it seems most opinions here either seem be rooted in inexperience how Gwent is played at top of the leaderboards right now.
I am far from being an Expert at Gwent, although I do understand the game well enough and concurrently I hover around 1500 to the top 2000 players, playing exclusively SK. And in my experiences from most of my games, Geralt Igni is BY FAR one of the top played Golds. Sure its most common in NR, (Most common as in, it exists in every single competitive NR deck besides Henselt.) It can also be played to semi success in some ST decks, although I would agree that there are probably better Gold alternatives for ST overall.
But does it need a nerf? It depends, I'd like to say no. But the problem with Igni is that unlike Aard, it doesn't require a 2 card set-up with Weather. Meaning it can't be countered, only predicted. The issue with prediction is that predicting means nothing if the deck you're playing can't use your prediction to your advantage. For instance, playing Monsters, it hardly matters whether or not you know you are going to get Igni'd. Last round, your cards have limited variability in how they can be played, and unless you have card advantage, which hardly happens as Monsters, Igni will have a large effect on the end of the match. And considering NR can easily get 40+ points last round, it's a Lose-Lose scenario, you can't get enough points on the board, and if you do, you get Igni'd. The only way this doesn't happen to Monsters is constructing an entire deck where Igni mayhem is limited. The result of which hurts deck variability in the long run and isn't the way proper deck construction should work to begin with.
Unlike Monsters this obviously is hardly an issue to ST because they have many ways to play around the card. SK has some ways, but again their entire smichk above 2k mmr is row stacking. They're forced to Row Stacked in most cases because their competitive cards exist solely in the siege row. Geralt Igni completely counters that entire play-style and even if the base buffs are staggered among cards, last round you're guaranteed most likely a 20 power curve in their favor. As a SK player, you at-least have the probability of getting card advantage the 2nd round from Spies, but even still NR is most definitely the faction to beat in my experiences. More so than Scoiateel.
And most competitive players only play NR and ST, both of which, Igni hardly affects them. NR because Igni can't affect their Gold Spam and ST because of Agility. So yeah, I get how most statements are "Igni is balanced." But for the other 2 factions, Igni ranges from just obnoxious playing as SK, to downright frustrating playing as Monsters.
Lastly, a good topic to bring up is that, I can guarantee you with complete certainty, out of result of the new weather changes, where "only one row can be affected by first light", row stacking your units will be the most conducive and the safest way to play Gwent for almost all decks. After this change, you can mark my words, unless some negative aspects are implemented to combat the prevalence of row stacking, both Aard and Geralt Igni are going to be most viable, and strongest Golds a deck can have.