Being fair, it's been one of the criticisms of 7th and 8th edition at large. The End Times rulebook just kind of turned all the dials up to ridiculous, and what little balance there was just went flying out the window. Being fair, the exploits have been there for a while - at the dawn of 8th edition, you could only throw up to 6 dice at a spell, because rolling a double automatically caused an Irressistible Force. Skaven had a spell which just instantly killed whatever it touched without any other rolls of the dice IIRC - but in addition to that, there is an item which allows any double to count as an IF, and for them to also roll an additional dice more than normal. So, if you do the maths, that's 6 possible results from 7 dice, where any double causes an Irressistible Force and cannot be stopped on a spell which instantly kills whatever it touches.
That works, right? Needless to say, friendly games and tournaments alike quickly cottoned on and banned it, but the End Times ruleset is just to allow you to have fun using whatever models you like, really - it is quite good for a newcomer to get into, because now, they no longer need to spend hundreds and hundreds of pounds on getting an army, then ages painting it just so that they can play with their centrepiece Griffon or Dragon or Daemon whatever you like, they can just say "I'm using this model, and this model and this model, this is my 1500pts army, lets fight". Which is quite a good sales pitch - as not only were big scary creatures historically (gaming-wise) notoriously susceptible to getting shot by cannons leaving your once proud griffon to look more like strawberry jam, but required at least another 1600pts of army to play - which at anywhere between 4-10pts for some basic models, was really limiting to getting your favourite model on the table (by which point they were dead in the first turn as well, so you might as well have not taken him, and just taken another 400pts of army.
In regards to how Winds of Magic work, I'd probably find it something along the lines of a trait like Zeal, Authority and Cunning - each turn, there's a random Winds of Magic event (which could be influenced by other factors, such as the strength of the Chaos Faction, or buildings/monuments in particular settlements/regions of the map), which increases or decreases a Wizard characters ability to cast magic spells - the higher this value, the more likely it is that they can cast a spell, and the more likely that any spell they cast is more powerful (say base 40% chance to cast a spell, each +1 magic causes +5% chance to cast spell, and +5% to the variables of the spells, whether it's range, damage, strength of buff/debuff etc). If there's an enemy wizard on the field, they could have an ability called dispel which works like a stance - rather than casting spells they are countering an enemies - which reduces the enemies magic skill by the magic skill of the user - hence in smaller battles, it might be better to just have your powerful caster sit in dispel mode and prevent the enemies from casting, while your unbuffed units kill the enemy, but in more desperate battles, when you're forced to empower your puny human halberdiers with magic weapons and to force their bodies to become as strong as an Ogre just so that you can take down the Black Orc "Immortulz" that form Grimgor's bodyguard.
I can't really see the spells being much different from abilities as they are now, with the exception of a few targeted ones like a fireball you can tell the caster to shoot at rather than just relying on autoaim or having said fireballs working as a shooting attack.