We have basically three tiers: heroic, epic, and legendary. The xp available to level in these tiers is entirely out of whack, and epics are absolutely the worst. Here's the basic math. Assumptions are xp for quests and raids unless otherwise noted, all difficulties on elite unless a solo quest, no sagas, no pots or other xp buffs.
Heroics:
1,926,280 total quest and raid xp available
Lives 1-3: 101.38%
Lives 4-6: 67.59%
Lives 7+: 50.69%
1,831,552 total xp quest available without raids
Lives 1-3: 101.75%
Lives 4-6: 64.26%
Lives 7+: 48.20%
Epics:
2,420,602 total quest and raid xp available
29.34%
2,257,435 total quest xp available without raids
27.36%
Legendary:
5,660,993 total quest and raid xp available
71.66%
4,730,413 total quest xp available without raids
59.88%
This is a huge discrepancy, and it matches my experience leveling. Heroics are easy to level in - I generally run low reapers for an extra xp boost through all my leveling, so that plus my other xp bonuses (30% pot, VIP, guild, etc) plus sagas mean I can choose to run the quests I like best and change it up if I get bored with no realy slowdown. It's a decent experience. When I hit epics, it's like hitting a wall. There's not nearly as much content, so I'm stuck running the same quests (some of which I don't enjoy as much), or I have to slog through a longer process (still not enjoyable) or resort to slayers (which some enjoy, but some of us want to gouge our eyes out afterwards).
The rush to raise the level cap before epics were fully fleshed out with quest content is, in my opinion, a mistake. But it's a mistake we're already on the road to, and no one is gonna turn that car around. With that in mind, my suggestions would be:
Option 1: When new content is released, instead of releasing a heroic and legendary version, release an epic and legendary version.
This allows the legendary content that will be necessary to be built up without neglecting epics. I think this would be the best scenario, as heroics really don't need as much right now.
Option 2: Significantly reduce the amount of xp needed for an epic life.
This honestly is, to me, less good because epics desperately need new content for variety. But it would be better than the situation now. It would have to be a huge reduction, though. To match the experience of a 7+ life toon in heroics currently, it would need to drop to around 4,600,000 (using the no-raids numbers, since I suspect that's most people's leveling experience).
I'd really like to see a change so epics aren't as much straight drudgery. Heroic leveling got way more fun the more content we got. I want epics to feel the same.