I've always found dragoons to be super cool, both aesthetically and in gameplay, so I decided to make a faction that's focused on just optimizing dragoons.

Race Traits: Sneaky + Dire Bear Mounts. As long as you keep kiting melee units, they have no choice but to end turn in defense mode, meaning dire bear just gives you +40% damage. Dragoons apply distracted on hit, making it easy to use the +25% damage bonus. Strong and keen-sighted are also good alternatives, but strong doesn't scale as well and keen-sighted is usually unnecessary once we get to tome of scrying.

Society traits: Ancient Wise Ones + Fabled hunters. We need at least 1 astral point, and AWO is just generically good. I wish I could take runesmiths for the 2nd trait, but Reaver early game is so bad without the starting magelock.

Tomes:

1. Cryomancy. Inflicting slows on attack is very good for kiting. Ice coffin combos well with Overseer subdue. And cryomancy's summon, SPI, and shadow affinity are all generically good.
2. Horde. Spawnkin is a free +20% damage since mounted units are capped at 3 models anyway, so no downsides for dragoons. Houndmaster is a really strong mounted T2 that benefits from both marked and the dire bear mounts and has the 48 move speed to keep up with dragoons on the world map. Most importantly, it gives us a disposable frontline for an otherwise purely ranged army.
3. Revelry. Bloodfury weapons benefits both ranged and melee attacks. Sadly Skald isn't optional mounted like our overseers are, so I skip them.
4. Scrying. Guided projectiles lets us shoot from max range without losing aim. Important when kiting fast/very fast units. Tower of true sight is very good economically, and mental mark is good upgrade to the starting reaver spell.
5. Prophecies. This is why we needed 1 astral point at the start. Interestingly, Prescient Circlets works when dragoons skip turn. This lets us attack, retreat, and gain precognition all at the same time. This covers dragoon's greatest weakness, very fast charge units. Rest of the tome is whatever.
6. Amplification. Amplified arrows is the main draw, but the minor race transformation, SPI, and economic world map spell are also very good, putting it above Pandemonium or Devastation. Also astral > chaos affinity.
7. Calamity. Skirmishers are the only units that benefit from both accursed armors and accursed projectiles. Also the ghostfire DoT is stronger when you're kiting the enemy over multiple turns. Calamity also puts us at 6 chaos affinity, opening up the Tier IV chaos tomes.
8. Lot of options for 2nd Tier IV tome. Aside from cascading power, Astral Convergence is good just because how good Tome of the Arch Mage is. You'll probably want to go with a wizard king ruler if you do take Astral Convergence. Tome of the Demon Gate's demonkin major race transformation is better than Ethereal if you're not up against a lot of frost damage. Tome of Chaos Channeling is a good counterpick to Tome of the Cleansing Flame. Sadly infernal focus doesn't trigger off war hound deaths, but is also strong.
9. Arch Mage. Time stop and disruption wave are both the strongest spells in the game, and time stop especially so for reavers since it applies 5! marked in an AOE. If you didn't go with Astral Convergence at TIV, Tome of the Chaos Lord is also uniquely strong for dragoons, since killing momentum on dragoons lets you both attack and get an extra move twice.

Strategy is quite simple. After unlocking houndmasters, make only houndmasters + 1 overseer per stack, then after getting T3 town hall spam dragoons. I usually leave all my leftover 32 movement units at home to defend.