"A single +2 minion should be REALLY hard "
Ouch. That's going to hurt.
Let me explain why... I was recently in a group, 30 controller, 30 blaster, 30 scrapper, 29 blaster. Good group, had fun, played for hours. We had a mission, Nemisis vs. Rikti in the sewers. When we rounded one corner two people died almost instantly. We had run into a group consisting of 2 level 30 Warhulks, 4 level 32 rikti Lts, 2 level 30 nemisis Lts, and about a half dozen minions. I think that there were probably two spawns very close to each other. We took them, after regrouping and planning for a bit. But under the '+2 is very hard' idea we would have been so challenged by that group that we might not have been able to finish the mission.
If you want to develop the '+2 is very hard' you need to be aware that the levels of some things in missions are beyond, sometimes far beyond, the stated -1 to +1 levels that are supposed to be in there. At level 20 my controller had a mission with a level 23 Skyraider Lt as the 'boss'. At level 28 a timed mission with a 32 Nemisis Lt as 'flavor', and another mission with a 30 Rikti boss. These are only a few of the 'boss' style mission mobs that seem to have hardcoded levels, no matter what level the player is when they take them.
Having to fail a mission, or quit it and level up twice in order to finish it, because of a hardcoded mob level, is not fun. Alternately running through a mission and finding the 'boss' is a Lt three levels below the rest of the mission is a bit amusing, but not the least bit challenging.
Lastly, alot of controllers and defenders already find anything +2 levels above them to be very challenging. Alot of these people would like the option of not having to absolutely depend on groups to do a mission or level faster than once a month. In the 26 to 32 range the non-damage oriented classes start having issues with the amount of time it takes them to do anything without a group.
More and more my non-damage characters are starting to not feel like heroes unless they have a blaster of scrapper to group with. Is this intentional?