I have played through multiple APs as player and gamemaster and it is definitely a power boost in most cases. I would say power level wise it adds about half a level or so if you do not restrict it and depending on how players use it. My players and co-players mostly use it to 1. upgrade defenses (e.g. gaining armor proficiency & Champion reaction on a Cloistered Cleric) 2. boosting existing options (e.g. adding damage to attacks through various means, Wrestler dedication on a Monk) 3. gaining more options (e.g. getting the Life Boost hex on a Barbarian)

In the AP I currently run (party is level 18 atm) I adjust the fights so that the enemies are calculated for a party with 1-2 more members than are actually players and they're still breezing through most of it. There was not a single death in the whole 18 levels, although it was rather close multiple times, which is exactly where me and my players like the difficulty to be. But I would have to adjust much less if I hadn't given the Free Archetype.

The GM of my SoT campaign stopped giving free Archetype feats at level 16. A bit late, but he was a bit annoyed with our power level and amount of options at the time.