Here's a Kiera of a guild member of mine.
That's 20k MAG before accounting for any additional MAG that can be gained from in combat auras, and without her own aura buffing herself. With the self-buff, it's 24k without accounting for ally auras that add more MAG. Lucille can reach these numbers too, since both Kiera and Lucille are Valiants. Most players in the top 50 arena run units with 19-22k Attack, or 16-20k defense, and 18-20k attack rangers/shadows with 75% crit cap.
You claim to have done your research. Maybe you haven't seen this thread yet, or know the lengths people go to to reroll their 6* gear stats to give +10% or more on the primary stat of EVERY piece of gear.http://www.forum.playvaliantforce.com/v ... php?t=3984
This thread contains what were considered "world records" for attack, magic, defense, hp values for different heroes about 3-4 months ago, BEFORE insignias were released.
The "ridiculous numbers" you claim are impossible, are in fact quite normal, even more so now that we have 5* insignias each increasing stats by a further 2k-3k easily. With the first Raid 2 sets coming out once guilds beat this ongoing Guild Raid 2 (it reset this morning for the second raid cycle), Raid Set 2 improves on Raid set 1 by nearly some 2000-3000 stat points, the numbers will grow again.