OP is a matter of perspective. Compared to the meta, nothing is OP right now. All of them have exploitable weaknesses.
Greatswords are a bit boring and linear to play against but that's about it for me.
partci's suggestion about enforcers might be the best middle ground we can find. But generally I am against the change in general, I liked the enforcers when they were retroactive for the simple reason that while in a utopian meta (or just pre-midwinter) they'd be too powerful, in the meta where point spam replaced engines (dwarves, bears, etc), removal was not such a big deal. This is proven by the meta reports, as spies had a winrate lower than 50%, and were dominated HARD by Dwarves, Eithne, Machines and Bears, while Alchemy and Reveal also stood a decent chance against them, the former due to vipers and the latter due to scorch abuse.
As such, the change in retroactivity nerfed a Tier 2 deck (check every meta report since midwinter. Spies were nowhere near as good as the top tier decks) to the ground. In my opinion, the point spam problem should have been solved BEFORE the removal problem. Changing the importance of locks, the function of vipers and then the enforcers to promote a healthy interactive strategy. As it stands now, we have a meta in which spies just don't fit. They only barely fitted before. That's all
Reveal needs to go back to the drawing board, the way it works is just counter-intuitive, it will never be viable as long as it's so reliant on the hand and a decent draw. You cannot include deck-to-board thinners (Joachim De Wett, Vilgefortz, even Last Wish can be dangerous) as they will always have at least one bad option (Fire Scorpions, Golems if used early, Daerlan).
Vipers would, in a Utopian setting, better function differently, but right now, they are the ONLY Nilfgaard viable deck for competitive laddering. Fix the point spam and excessive Skellige revivals first and THEN we must look into changing Vipers. By all means. This will need to happen. But not now. Gwent is a game in which you can't change one thing and leave everything else untouched at this point. Changing Vipers when the game is as it is right now, literally means killing the faction and its only viable deck. It's certainly not the only thing that needs to happen for all you pre-midwinter nostalgics, if we are to get the game we'd all like to have.