The games is not too easy, because I cannot solo +4/8 without inspirations. I can solo +4/8 with one character, using inspirations, but he is Tier 4 across the board. That seems like it's just right. I cannot say he never dies, because if I do not keep up with my combining, and judiciously use my buffs and self heals I can die.
Things have to go just right.
With that said, I usually run that one character, when I use him as a farmer, at +3/8 because I do not need it to be THAT challenging.
It is challenging enough with my lesser characters, running at lower settings. I feel like this game is right at its sweet spot for most tasks. Some characters cannot solo well. I look at defenders, at least the sets I have chosen. 0/0 is a slow slog just soloing, but defenders really shouldn't solo. With that said, when the defender gets on a team of 8, I feel he looses his identity, he blows through content and doesn't need to use his powers correctly. So it's just not as fun for me. Therefore I just do not play defenders all that much. I dont know if this is a popular opinion, but it is what I observe. I play this game by feel, not by number crunching.