The game rules do state that players are expected to get Potency and Striking on their Weapons at certain levels, and Potency and Resilience on their armor at certain levels to keep up with the monsters.
Take a look at the chart in the
Automatic Bonus Progression variant for an at a glance of what built-in bonuses need to be covered in an itemless game (its also listed in the text of the treasure section of the core rulebook, but in less detail). This was the result of playtest feedback indicating people wanted items to be required part of progression, so the linear math was actually just offset at certain levels to provide that requirement.
Interestingly, it includes the skill item bonuses certain items have, and the Apex Items that boost ability scores at high levels.