Part of the issue is the principle that veterans are always re-fighting the last war.If you plan to start with an Adventure Path, use the later ones. Avoid Age of Ashes and Extinction Curse as I think they were written with the assumption of veteran players with tactical mindsets and are not ideal for new players.
In 3e/PF1, Challenge Rating and Encounter Level were jokes, particularly given the synergies possible with ten years of dubiously balanced options. So one of the selling points of PF1 adventure paths was that they were written by people who knew the system and could provide an appropriate challenge anyway.
In the early PF2 APs, this "hardcore" mentality bleeds through, but PF2 is balanced enough that this leads to an overcorrection. In addition, at least some of the APs have fairly big dungeons where you're supposed to do it all in one go, and even though PF2 is fairly generous with recovering hit points once you get the Treat Wounds engine going, you still don't have enough spells and such to handle that.