What opportunity cost? And why can't caster epic strikes be better than heroic spells? After all epic abilities should be stronger than heroics ones and the best melee/ranged strikes hit harder than heroic abilities too.
Agree that hellball needs to be massively buffed to be worth at all, even taking a feat for it (for casters epic feats really are in short supply, so much stuff you need to take for dps and dcs)
when you let them be better than class spells then it raises a question of "Why is a rogue able to cast a better damage spell than a pure sorc gets in his spellbook" It undermines your class identity and then your class doesn't matter for anything besides how many caster levels and crit chance they give your epic spells and whether your class can get rid of immunity for your epic spells. Epic Strikes mostly fit the role of rotational filler to fill out gaps from your regular spellbook
I need to explain this outright right here in bold letters because I am going to go into MATH on average spell damage between some of the spells granted in epic destinies, I know that your funny sorc build gets bonus maximum caster levels with x and y, I know that class X does this and that.
But if you're comparing spells directly there needs to be a consistent base to compare them from so I am going to be calculating each spell off of the maximum caster level they achieve with just 34 character levels, no major forms and no class enhancements. Caster levels to specific elements etc. pretty much keep the patterns going except for Ruin, G.Ruin, Spirit Blades and Arcane Pulse which do not benefit from bonus or any caster levels. I need to write this out here as most every time I go into comparisons of spell base damage there's someone who chimes in about how their sorc casts at level 48 or something.
They share cooldowns and the funny thing is they're far from the actual strong spells in the epic destinies.
The thing is Magus of the Eclipse actually does give you a 9th level SLA (Zero Degree Comet matches iceberg) in t5 and conditionally ups your epic strike's damage to somewhere between an eigth and ninth level spells - on a 6 second cooldown for 5sp cost.
The overall base damage of Shardstorm level 34 is (27d4+2)x2 coming out as 486 an average base damage per shard - 2,916 damage per cast. Ruin intensified greater ruin conversely is 2000 base damage and Thunderstroke and Iceberg (and Zero Degree comet) at level 34 are 850 base damage on average.
Holy fireball however is kinda pathetic for a t5 SLA at 405 base damage per cast in comparison but that's aoe and only a 10 second cooldown.
3 chord Echoes of Discord is 486 base damage while Strike a Chord is 351 average base damage, for a 2 second cooldown you pretty much hit whenever you have all your stronger spells on cooldown that's pretty respectable - especially considering the dearth of sonic spell options.
Now here's the thing, one balance issue between martial strikes and spell strikes can probably be found in the fact that while spells are gaining half of your epic/legendary level in cl/mcl - Quick Cutter and Pluck of a String are getting a full 34 character levels of added damage...
...but in truth one of the biggest discrepancies is simply that weapon based styles act constantly and they are not just
only their active attacks.
DPS is an average of damage performed over a period of time from start to finish of combat, it is not in fact how much damage is done in a single second, if you want actual DPS you do not focus entirely on a singular hit you only do every 15 seconds and ignore all your other options.
Caster DPS is struggling as a whole, it can not keep up in action economy and can not keep up in overall growth of modifiers from itemization, the caster level system going into epics and legendary is flawed and the scape of spell design needs reevaluating.
The leveling experience overall is bizarre and skewed towards casters, a large part of that is metamagics and bonus caster levels frontloading a lot of power and then as your spellpower grows and you reach MCLs the proportion metas and CL bonuses give you start to fall off but another is simply how frontloaded spell damage is, every 'good' spell does damage upfront and this pattern of not waiting and just doing all your big damage upfront created a gamestate where your rate of damage doesn't matter as you can always just wait to oneshot everything at the start of the next fight.
For many players leveling is 99% of the game and casters are still and always will be kings of leveling because of this frontloading, this is a large part of where the animosity towards casters came from - everyone knew that when it came to endgame dps casters fell off but for the majority endgame dps doesn't matter.
Meanwhile because melee and ranged weren't so capable of oneshotting their damage consistency has grown, and to challenge the DPS ranged and melee are actually capable of enemy health pools at level cap have grown too.
Grown to the point casters don't oneshot anymore.
The answer I feel is not to ask to oneshot again but to ask to get to play the same game that melee and ranged get to, to have consistent damage, because raid bosses are always going to be built for facing consistent damage.
More DoTs.
As an aside though, the r7+ spell damage penalty either needs to be the standard for everyone or scrapped, it hits everything except front number damage so even imbue and proc focused builds are hit by it - it was a nerf for a game where only DI's dragon breath mattered to casters and this is simply not the same game anymore.