A great idea that desperately needs attention is the power curve of 60+ individuals.
Only allow a level 60 to be paired with players +1/+2 to their level, and -3/-4 to their level.
This applies for all levels 60+, with the exception of 70, which cannot be paired higher.
The curve of power and grinding is immense once you hit 60. Just starting, a level 60 is probably sporting improved runes. A level 70 to 65 would utterly decimate them, due to having more time to grind for runes. As a level 64 (Almost 65) The power curve is undoubtedly, undeniably extreme. I am facing roster after roster of 3 level 70s who's rune are legendary greater or even superior. This is not fair in the absolute slightest, nor any fun at all to play the gamemode.
Dodge chance. A level 70 will gain far more dodge chance being attacked by a level 60-66. If an MK with all superior runes can dodge 6 times in a row, where is the fun in that? Lower levels should not be hindered by this, or so unfairly paired in the first place.
What about level 70s?
As a 70, you should be expected to compete at the highest level. 69+ pairs sounds perfect to me, as you cannot progress further in the levels currently.