It's not about having a win button so much as it is having a viable playstyle people enjoy. There's a win-button build in every major skill tree, you just need to know what skills and gear to pick. I don't know how it is in 1.07 because I honestly didn't want to face the new issues, but prior to that I've seen a really nasty 10k HP Alchemy Build with 3 decoctions + a few potions focusing on strong attacks that was basically "press Y and kill everything. Oh, and you still got some really powerful bombs, in case you need them".
All big medieval RPGS offer a magic playstyle nowadays. The Witcher 1 didn't had it, as you would only get your signs strong enough (and have enough stamina) to deal with enemies solely on their own by the end of the game. On the other hand, playing The Witcher 2 on Dark Mode with upgraded igni, yrden and heliotrope sign was a lot of fun. The Witcher 3 had it right. Sure, Witchers are not mages, but they are not bothering with being true to the books story, hell they aren't even bothering with being true to the previous game choices, why bother butchering a gameplay aspect that offers players some diversity? Why create a whole magic skill tree if they don't want you to build around it?
It's not even about Igni being weak, as the regular version remains pretty decent. It's about breaking a skill that should be a logical progression and calling it "balance". Even if the regular Igni burn was as weak as the firestream version, people still wouldn't use it (they wouldn't use Igni at all tbh, let's face it, Yrden and Aard are murch better for CC. People use Igni for the damage, while providing some degree of CC) over the regular version, simply because the firestream will leave you exposed while the regular provides a quick cast. This change essentially broke one major skill. Imagine if something like this happened to Whirl, would you be happy? I know I wouldn't.