In my opinion, the point of RPGs is drama. Put the PCs in a situation where they want something, but getting it will put them in danger, and then we see how they overcome that danger. Combat was the original element in the genesis of RPGs, so it's pretty well figured out, and I've done it so often I can tweak a fight scene on the fly to keep tension high and lead to a satisfying conclusion. Handling long-term or long-distance challenges, however, has received less attention, and maintaining tension is harder. You've got to factor in how much info the players have, what options they have, how urgent the situation is, and so much more.
When a PC kills a villain in one round or hits a bunch of foes with a fireball and does more damage than a fighter could ever dream, that's just an issue of balancing the numbers (and I'm working on that for my own system). But when a player gets to say, "Okay, my character is going to have influence over the plot, without being in danger," you run the risk of ruining drama.
Basically, taut storytelling is endangered when PC agency extends farther than the threats can reach back. This can be caused by PCs having magic, or high tech, or allies.
So as I try to balance the magic system, my goal is to let spellcasters exercise control on the story, but only at the right scale. Initially I erred on the weak side, but I'm going to try to scale things up. The vague baseline I'm working from is that 'heroic tier' (1st - 10th level) mostly works in the immediate world. You can influence stuff you can touch pretty significantly, stuff within ~100 ft. a little bit, and stuff further away but within sight occasionally. Paragon tier (11th - 20th) extends out farther, so you can easily affect stuff within 100 ft., have mild effects anywhere you can see, and occasionally influence the world miles away. Epic tier (21st - 30th) gives you the ability to affect anything you can see with ease, moderately influence a small region, and occasionally affect any point in the entire world.
Some tricky areas:
Summoning, if you let a creature roam far, is sort of like splitting the party; it's a pain in the neck for the GM, and leaves most of the party bored. (Likewise long distance mind control.)
Teleportation or invisibility or flight can remove the GM's option to include scenes like dangerous travel and evading guards. Also in combat it keeps you from being in danger, which while you might like it, is bad for drama.
Divination, if it lets you learn secrets from the comfort of your home, cuts out the option of having the PCs explore to find important information.
Creation spells, healing, and heat/cold resistance, can make it so starvation, thirst, exposure -- even death -- are never problems.
All these areas I'm trying to make available, but at the right power level so you have tools to make the game more interesting, instead of cheat codes to skip the whole level. I think it's possible to have a non-broken magic system that is flexible, in that you can do all kinds of things, instead of being limited to a handful of spells in a given day, but you have to place careful restrictions of magic that grants narrative agency without hazard.