It just isn't and you can see it very clearly in the fact that players have started to forgo fun, flashy lores like Fire in favor of wind spells that still work, stationary vortexes and impactful debuffs. Burning Head is probably the one most people will be familiar to, Wind of Death also, but I want to point out that Black Sun of Xereus* is the greatest and saddest waste of winds of magic I've seen yet. I get that magic in general was nerfed because of the multiplayer, but the nerfes are so inconsistent that it's just not fun to use most lores of magic at the moment. Some are good still, I don't think I need to mention the lore of shadows (which is not op since the nerf to pendulum, btw, it just deals damage and the other lores... don't) but others like the lore of Tzeench can still pack a punch, but a lot of them NEED to be fixed. Here are some ideas:
-Increase the cost of certain spells and add to most casters a skill to make it cheaper in campaign; that way it will be balanced for multiplayer and fun/not useless in campaign. A lot of caster heroes run out of skills to get by level 50 anyways.
-Make non-stationary vortex spells deal more damage. The only one that still performs well is Tzeench's Firestorm and that's only because it deals a lot of damage in the point of casting as if it were stationary, but spells like Firestorm or Black Sun deal less damage than spells costing one fourth of their value
-Return to non-stationary vortexes the hability to be pointed in one direction, even if afterwards it can just go wherever it pleases
-Increase the duration of buff spells and some non-stationary vortexes, as the duration at the moment in most cases too short to gain any value out of it.
-Set a clear difference in how magic works between campaign and multiplayer battles. I'm not sure if this would be too much work for CA, but the easiest solution would just be to have different stats for spells between the two. In campaign Wind of Death can be the blob destroyer that was meant to be while in multiplayer it can loose a lot of power to enforce the use of better units and micro strategy rather than relying on magic to do your dirty work. Win Win.
*Seriously, try and play a campaign with archaon and spam Black Sun, you will understand why I use it as my example for most of problems magic has atm. You can also waste your winds of magic casting burning head and feeling disappointed. Then turn around and cast anything from one of the gods of chaos's lores with another character to see the difference. Let's make magic powerful and fun to use again, please.