I think you're falling into Plug N' Play Magic syndrome. This is where you want magic, so we add magic to our world (medieval in this case) - and now it's awesome, right? But you can't ignore the implications of magic - let's look at an actual example.
The Elemental Knight.
So I have a knight. Now let's make his armor stronger (earth), but make him faster by enchanting his boots (air). And let's give him two swords because dual-wielding is cool, one enchanted with fire and one with water (chilled to ice). And now we have a super fast, super tough guy wading through the battlefield, cooking other knights in their armor and freezing peasants. And your reaction is "That's awesome!" right?
And now we run into the problem with PNP Magic, and that's that it doesn't hold up to critical thinking. I mean, think about what we have for the above: super strong materials, a source of heat, and a source of water. Which means that realistically, the wizard who enchanted all that stuff should be making a better use of his time and create an Elemental Steam Tank. And now Elemental Knight is Elemental Tank Driver, which while cool isn't really what you're going for. You might think you can avoid this because the steam engine wasn't invented yet, but consider that Romans experimented with steam power. If they had magic to help power it, it probably would have happened almost 2,000 years earlier.
The fact is that technology drives design, and your tech (magic in this case) is going to impact whether or not shields are useful. You can't just ignore it because you assume it's going to be an arms race where things cancel out.
Now, there's nothing wrong with PNP Magic if that's what you're going for, and it doesn't prevent your story from being enjoyable. But in that case you might as well throw your hands in the air and use shields just because. So let's look at ways magic could make shields viable.
The problem with shields
In our reality, the problem with shields is the weight/effectiveness ratio isn't great for knights. If you make it big and strong enough to be useful, you can't carry the thing around. Make it light enough to use, and it's too small or weak to be effective. Magic can help this in several ways - stronger materials? Now you can have a big wooden shield that will hold up to another knight's blows, and suddenly our equation has changed - maybe it does make sense to carry that shield.
Another possibility is versatility. This depends on your enchanting system, but consider that maybe items can only be enchanted so far, and there's a lot of enchantments you want to put on armor, right? Beyond making it stronger you might want to make it self-cooling, self-repairing, summonable, operates in water... there's a long list. But a shield is pretty much just a shield - you can make that thing as tough as possible given your constraints. So maybe with magic it's not the case that a knight's armor can take the same blows a shield can - maybe your shield is much more effective at stopping blows, and the armor is there to keep you alive when you mess up.