I'm also on the "bosses are too tough" bandwagon. While I realize this boss change really hasn't impacted lower levels, I see some great examples of how it should be at lower levels.
In the hollows, you eventually have to go up against Frostfire, then later against Atta. These folks (Atta for sure, maybe not Frostfire), are classified as Elite Bosses. Tough as nails, impossible, or nearly so, to solo unless you outlevel the mission, and a great way to end a storyarc. I'd look forward to things like this being incorporated into the end missions or important missions of a storyarc. I have no problems having to get a group to polish off villains like that. It makes sense.
However, it seems to be rather insane to have to get a team together to fight some random street boss of whatever faction, or even to have to get help to take out some relatively unimportant named boss in a mission that I receive from a contact whose story arc or series of missions isn't coming to a close. Yes, they are 'bosses' but they aren't the elite, team stomping villains of a massive story. Using inspirations, tactics and maybe a pinch of luck, a hero on the default settings, pretty much regardless of build (and I know there are some builds that can't solo period; that's a person's choice) should be able to take down "named boss 09" in his mission. Sometimes that boss might take round 1, sometimes a person might need to run; but they shouldn't, on a large scale, have to recruit a team to take out villains of that stature.
Elite bosses, monsters and archvillains, definitely; and that's fun. They are 'epic' and it makes sense for a team of heroes to band together for them. But removing the ability to solo for a large portion of the populace is a painful way to remove enjoyment from the game for people. The slider bar is a great tool, for the elite player with mad skills, but for normal people who want to be able to pop on for an hour or so, do a mission and log off, the game is being removed as a viable system.
Personally, I play for the missions and storyarcs, and while not everyone may play this way, it is removing this as a, for much of the game and its players, a viable option for playing. It is not always an option to get a group, nor is it always desireable. And street hunting is not a fair option to the masses, and in my opinion, street hunting is alright once in a blue moon, when you are out of missions, but for me this is not why I play city of heroes. From what I've read here on these boards, many others feel the same way.
For the most part, I've had no real problems with the changes, except the one involving bosses. Again, I have no problem with certain bosses being buffed up to the status of elite bosses and taking a team to battle, but your standard (as a crappy example) bone daddy or damned, or other unnamed boss, and your "Tommy Two Thumbs" of the Family are not guys that an entire team of heroes should have to combat.
I would hate to end up quitting a game I really enjoy because I'm unable to complete my missions for the most part unless I can find a team to do them. And that is simply neither reasonable or satisfactory at some times for me.