If you get quite well geared you can take many many 'heroic' single and double mobs, greens especially, and there are lots and lots of one and two up heroics.
Where I think there is a problem is simply in communication.. heroic means nothing in this game really, the arrows mean far far more. A straight no arrow heroic is manageable by a level con average player for sure. I guess mine could take a level con 1 up alone.
In a Duo we take level con 3 ups and regularly 3 level below 3 ups with support mobs (note how often support mobs are non heroic downs)
And there are OH so many mobs of 3-4 level con 2-3 downs out there easily soloable.
I cant see it at all, if you get out of the "curly brakcets means group only" mindset. It doesnt have to!