It's easy to call it discrimination when it affects you and you are offended, but try and see some perspective for a moment: Mages have a skillset no other "class" has so far - multiple attacks and helpful spells. Ideally, were this game not pretty much a work in progress, every class would have it's own usable skills, some of which would also probably negatively affect events somehow. I strongly prefer to play mage over any other class, and I don't see this as discrimination. All that is expected, is that players respect the event's rules, when there is one. If every event has the same rules and things prohibited, then it would be more like discrimination in my opinion - I would not enjoy if no events ever allow any other magic besides lightning or flare dart. Much as I love the whole "looks like a dog, barks like a dog" quote, being convinced that something is a dog does not necessarily make it a dog - I can argue a sweet case for why a horse is a dog, but at the end of the day it will still be a horse. I don't say this to mock your feelings or argument - only to point out that while you can very clearly see something as discrimination, it is very easy to misunderstand someone's intentions. Prsm simply feels that certain spells disrupt events, and said as much during the event AFAIK. We all have our own ideas of what we feel is unacceptable during an event, and while this may not always please some players, there is no standard set of event rules, and specifics do come down to the GM hosting's choice.
What do you consider to be "stating the rules clearly before the event starts"? Because that is what global announcements are intended for in that situation, and you said earlier that you don't think that is good enough, since players often don't pay attention to the general tab. While this may be true to an extent, the players attending the events clearly saw the announcement of the event, so I don't see this as the best excuse. To me, the global announcement is the most noticeable way for a GM to communicate with a crowd, and that seems rather crystal clear to me.
For the record, you never know when you may see an event geared to give archers or warriors the disadvantage

.
Tiana wrote: I apologize if I gave anyone the impression that BC is the troll-king of the GM's. That title is rightfully held by mrgrey

<Mistakes> you are too difficult to troll
<Frost> Germans have Chess Boxing. English have Cheese Racing.
<Frost> I'm slightly terrified what the Russians consider violent sport.
<o11c> chatroulette
<Jaxad0127> YOu can't grab yourself.
<Jaxad0127> Elenore explicitly prevents it.
<Mistakes> speak for yourself