You're right. I'd say we will have a full perspective on both God's mercy and his justice. It's not that his mercy is good and his justice is bad; both are good. And we will know that, and we will be happy in his execution of justice.
From our perspective now, we think of people here who can avoid destruction if only these poor souls will repent. We want them to make the right choices. But that opportunity closes at death. The situation is different at that point.
Just as we don't "feel sorry" for demons who made their definitive choice long ago, neither will we feel sorry for others whose final choice was hell. Certainly not when we are perfected in mind and spirit in God's presence (rather than viewing everything from our current, carnal, earthly perspective).