How does perception work?

The reason perception is not that important, is that it only grants +1 to accuracy per point above 10. Whether your characters sport 30 or 35 accuracy (assuming 15 perception) doesn't make much of a difference, the 15% dmg increase from might or 15% atk speed increase from dex have a far bigger impact.

You are correct though, that accuracy is the biggest problem on higher difficulties, however perception is not the way to get it. You still should have a character with very high perception (18+) to detect secrets and traps. (note: this only applies to PoE 2, in the first game, mechanics skill is used to detect secrets and traps.)

The wiki has a comprehensive list of accuracy sources. Here are some tips:

• use accuracy bonus weapons and specialize on them (spear, rapier, dagger or club)
• wield single one-handed weapons without a shield. If you use a rapier without a shield and specialized in the weapon type, this adds a whopping +23 to your accuracy.
• possibly: use accurate 2 weapons (+8), instead of fine (+4, but higher dmg).
• Paladin aura (+6)
• use accuracy gauntlets
• Priest abilities: +5 from blessing spell (lvl 1), holy radiance with inspire talent (+10), devotions of the faithful (+20, lvl 7)

Finally, reducing the opponents defenses is also very important: ciphers are very good at that. List of afflictions. Prone, blind, stuck, weakened, stunned, paralyzed, charmed are all available pretty early and debuff the enemy significantly.