As far as Stealth goes do not forget about Follow The Expert which makes things still pretty difficult, but doable.
That helps mitigate the "I'm untrained" problem, but that's not really the main issue with Stealth.
In our experience, Stealth doesn't work in the context of a group game. There are many facets to this.
The main issue with Stealth is that your group's stealth is only as good as the
worst roll of the team.
What that means in practical play is that unless you have an ability (magical or otherwise) that let's you make a single roll for the entire group or gives everybody a
ridonkulous bonus cold hard mathematics pretty much say a hard no to everybody tagging along. In other words, Follow the Expert can easily be a trap choice. (A "trap" choice is a choice that seems reasonable enough on the surface, but turns out to actively make your situation worse)
Note I said "can be", not "must be". If you need to make the rolls anyway ("Everybody make a Survival check to see how you cope with the grueling march") obviously Follow the Expert is a nice upgrade. Plus, Bob failing on a Survival test might make him fatigued or some such. When it means the whole group is dragged into danger ("the avalanche triggers on a failure") the situation is comparable to Stealth, but in most cases a failure has personal, not group, consequences.
I'm instead talking about cases where
not Following the Expert is the better choice, such as where having just a single character scout ahead, or indeed, where not bothering with Stealth at all is the key to survival...!
After all, the old adage "Never split the party" has never been truer than in PF2 - the game is simply not equipped to handle a situation where a single character is caught red-handed by the big bad. Keep in mind that very much unlike most other editions of D&D, in PF2 even a moderate encounter is likely to be a
practical death sentence for any character that is caught snooping around, especially given how your bad Stealth check is used as your equally bad Initiative roll - you need actual luck to survive until your first action!
More generally, for Stealth to be worth it needs to be
reliable and the payoff needs to be
worth it. If you only fail on rolling a 1, that passes for reliable in a D&D context. If you can bypass monsters that won't just bite you in the back later on, or you can set up a significantly more lethal death attack than a regular combat round's worth of damage output, that passes for worth it in a D&D context.
In our experience Stealth is neither reliable or worth it. Especially in PF2 where Stealth is a joke for purposes other than "me gaining sneak attack". (Even fully loaded with bonuses, you still struggle to reach more than just maybe a 60% success rate against any monster high level enough that you actually want or need to hide from it) And the benefits to an ambush are tuned down to the point where they're nearly non-existant in PF2. Sure your great Stealth check might allow you to take a special action, deal a couple of extra sneak damage dice, and act before the monster. But you can't down even a monster of your own level with that. But the monster can certainly down you!
I'd say that you basically need a different game engine to enact your Assassin's Creed fantasies.
And then we haven't even discussed the elephant in the room: nobody wants to sit on their hands while one or two players experience the adventure for themselves. D&D is a group game, which pretty conclusively rules out Stealth as something other than a rarely used niche activity.
