Logically speaking here:
Keeping old cards effects and making new ones trash is as much as bad as nerfing them all. Plus, some of you are not paying attention to what the Russian CM said about such changes. I'm gonna quote here again, please read it carefuly.
And this changes will affect not only the boss cards, but also other cards with high demand, falling from low-level monsters. The main criterias were two: a card and monster mismatch (for example, the card strongly affects pvp, and the monster is found in the PVE location and/or low level) and the general imbalance of certain cards
If you read it right and get the meaning of this you'll understand they're talking about a bunch of cards easily obtained due to low lvl monsters and etc. And for such statuses and impact these cards should be harder to get. They also are aware of how bad these changes can be and if they're ready to nerf 2 of the best PVP cards it's because they either have something else to replace or even better. At least is what i can get from this, but come on, what are the odds of they suddely nerf 2 cards and yolo leave the situation like this? And they won't change only these 2 boss cards, there are other regular cards to be changed as well (confirmed by Enya a few posts above) we just don't know if they'll be cool or nah.
The game is getting a new difficulty, we can expect harder mobs, places, quests, bosses and etc in order to improve our characters to fit new content. I also spent years farming these cards but if new and better cards come i'll gladly farm them and i doubt others won't farm them just to keep their current ones. We can only wait patch notes to make sure if we're getting trolled or if all this kind of stuff is going to make sense. We shall wait and see.