Is Hornet Queen only a break because it makes a bunch of small flier tokens? Green seems to be allowed to get flying on high MV rare creatures, like on the occasional green dragon.

Hornet Queen’s issue is that it’s too efficient in both creating fliers and in shutting down the opponent’s fliers with your own fliers.

"Do you feel like you are stretching evergreen keywords to too many colors. Reach used to be only green now white and red can both get it. Green gets flying in almost ever set now and even blue has haste and is getting vigilance."For reference, Mono-Green has gotten exactly 5 creatures with Flying in premier sets since the Tarkir block. Three are parts of dragon cycles, one is a callback to an iconic green dragon and one is Gilded Goose, which has 0 power and so mechanically is similar to reach. The claim that Green gets flying almost every set is very false.

FYI

If/when another mono green dragon?

There will be one when we do another cycle of monocolor Dragons. We do them about once a decade.

"Yes, Dungeons and Dragons debuted with exactly five dragons, one matching each color of magic. Four of their five habitats also match the Magic basic lands, only white dragons (whose habitat is arctic) don't." Not exactly- OD&D debuted with the Black dragon (swamps), Blue dragon (deserts), Green dragon (Forests), Red dragon (volcanoes), and White dragon (Arctic), as well as the Golden dragon which had no particular favored location. So, six dragons, two of which do not match MtG's lands.

FYI

When/If: Blue/Green Dragon

When.

Due to the prevalence of these cards in RTR, I feel justified in asking this: What part of the color pie is uncounterability?

Traditionally its red and green. Red gets uncounterable spells and green gets uncounterable creatures. When we do cycles though, we occasionally bleed for the cycle. For example, In Champions of Kamigawa, the green dragon in the cycle had flying even though green seldom gets big fliers.