Alteration's actually way more useful than people think, but yeah—the perk tree is weirdly front-loaded and then falls off a cliff. You're not leveling it wrong; the school just needs a specific approach to feel good.
The real payoff is Mage Armor (which you've got) plus the perks that boost it. That's your bread and butter for a pure mage. After that, grab the perk that increases spell duration—makes your buffs actually stick in longer fights instead of needing constant recasting. The staggers-on-hit perk is solid too if you're running Mayhem spells or anything that triggers it repeatedly.
But honestly? The reason people don't talk about Alteration builds is because it's a support school. You're not going to out-DPS Destruction, and it's not as flashy as Conjuration. What it does is make your character absurdly tanky and hard to lock down. Paralysis is one of the best utility spells in the game, and Alteration gets perks that make it land more often. Paralyze one tough enemy, nuke the rest with Destruction, repeat.
If you want it to feel less dead, pair it with Restoration for a proper battlemage—the durability stacking is ridiculous. Or lean into the crowd control angle with Conjuration. Alteration solo is a slog because the perks don't synergize into a thing; they're just scattered utility. But as part of a broader mage build it's genuinely strong.
What difficulty are you on? On Legendary the defensive stuff matters way more, so Alteration actually becomes pretty essential.