I totally disagree. I find that currently conquest is usually easier to get then either of these victories. If anything the other victory conditions should be made sooner but more competitive. Right now the other victory conditions feel like things you do if you are too bored to go for conquest.
The quest victory is all right because it makes you explore the world and fight tough monsters to win. The first quest could be easier and then they should get harder so it feels like something you work towards an entire game, and don't do in order to end a game you have already one. You could also add special rewards that make questing and exploring easier.
Magic though is just a generic civilization or wonder win right now. It really is what you do if your winning but can't be bothered to try and conquer the other players. In addition to requiring 1 of each shard perhaps the spell of making could also need for the casting sovereign to have a certain portion of the Shard Mastery output of all the players, say over half although the number would change depending on the number of players. The % amount of all players would be listed in the victory condition window. Shard Mastery would be granted by shards and various magical buildings. With upgraded shards and the current Forge of the Overlord buildings granting large amounts of Shard Mastery. You could even change it so each tower is a world achievement and unique and scatter them among the magic tech tree. Thus players going for a magic victory would have to plan it from the start and compete amongst each other to amass the most Shard Mastery and magic tech. This would be much more organic and interesting I think then the current system.
Alliance victory could also use some work since it mostly triggers when you conquer everyone but that one guy you allied with. That's not much of a diplomatic victory.