Here's what I think: You guys were entering epic Buying Time for 5:00 runs @ around 4-5k with a pot, maybe upwards of 6k/minute. This would let you go from 1 to 20 on a first life in six and half hours of solid grind, so figure 9-10 hours with breaks and whatnot. This is consistent with your "leveled to 20 in 24 hours" claim. (On legend build that would be 14 hours of solid grind, so still possible in 24 hours if you're crazy.)
That 4-5k/minute is NOT too much epic xp. It's only too much if heroic levels can get it. Your silly claims of 30k/minute do nothing but derail an intelligent debate on whether cannith challenges needed nerfing. They most certainly did not. All they needed was to prevent heroic levels from running epic challenges.
Right now in the game today it is pretty easy to maintain 4-5k/minute in quests sustained, for hours a day, every day, including time to rebuff every hour and run to the quests. (Some of those runs are long.) That's with just 5% cannith xp pots.
With that as the baseline for quests, the old cannith challenge epic xp of just over 3k/minute with 5% pots is probably too low. Too bad they double-nerfed that 3k/minute down to 800/minute, rendering cannith challenges utterly useless.
If the old 3k/minute with "free" 5% pots was restored right now people would say cannith challenge xp isn't worth bothering with because a) you can get better sustained xp/minute from questing and b) challenges do not give commendations of valor.