Yeah the problem with the feat based multiclassing in PF2 is that its just another of the points where PF2 designer stole 4E design without understanding it and with it took another of 4Es flaws and made it worse.
Feat based multi classin was in 4E because it allows to have classes be front loaded. So gaining everything needed to fulfill their role and not just instantly die on level 1. That is why level 1 in 4E is something like level 3-4 in 3E or 5E. This is not possible with level based multiclassing
PF2 took the design, but it is not really front loadet, so it did not make use of the advantage of the design. Meanwhile it keeps the weakness of the feat based multiclassing, (it feels weak) and makes it even worse!
- In 4E initial multiclass feats are strong
- They give a new skill training (which normally costs a feat itself)
- It gives as bonus one of the new classes mechanics in a weakened form which is worth a feat (like once per combat using sneak attack)
- It unlocks a lot of new class feats, so more options, which can have quite a bit of power.
- In 4E it costs a "general" feat not a "class power increase" unlike in PF2. So you do NOT have to give up on a class power increase (which is a new power or a level increase of a power), meanwhile in PF2 you have to
- The class options you can pick thanks to the initial feat, are as strong as in the main class! So you can pick with a feat a feat from the other class or exchange one of your powers with the power of the other class both of which are same level/power as if you would be the class you multi class in. Meanwhile in PF2 you even need to pick a lower level feat of the class you multiclass in.
- Also feats in 4E have a lot higher total power budget than they have in PF2, so they can have more impact. In PF2 most power budget is in the numbers (attack and defense etc.) or spell slots which are independant of feats
- On top of that class feats are dependant on one another, because they often represent a subclass choice. So you are dependant on picking some class feats even if they are weak, leaving less feats to use for multiclassing.
But in order to fix the "damn multiclassing is so weak that (almost) no one would ever pick it" PF2 added another of 4Es faults by having "free optional power". In 4E its character themes, which were added later, and give low level characters quite a bit more power, in PF2 the free multiclassing DOUBLES the class feats you get after level 1! And it does not bring any difficulty adjustment with it. This either means that multiclassing is sooooo extremly weak that it literally makes no different in power budget or that characters with free multiclassing are just stronger in a way which is not accounted by the system. This is one of the laziest fixes one could have implemented. Just give options which are too weak for free (as an optional rule) instead of balance them properly.