Exactly. If each Secundus was listed as having a few class levels or something, to differentiate it from other Secundi, then each would be a unique creature. But as far as I'm aware, they all have precisely the same stats.
Perhaps true. However, that still doesn't change the fact that Wildshape isn't going to suddenly grant you a bunch of personally chosen arcane spells that you had no prior way of actually knowing how to cast.
prior to the wildshape, you had no cleric or sorcerer casting levels either, a druid with sorcerer casting is ridiculous! but after the outsider wildshape, you
DO get
ALL ex sp and su abilities of the new form, you're preconceived notions of what a druid or anything else is goes out the window
simply ignoring that fact or claiming a case for a 'sane' DM does not mean that this can never happen at any gaming table
broken? sure, the best optimization of caster levels? NO, will it spark an agreement to not use this? probably.
also, what about a gestalt game? druid, planar shepherd// sorcerer now can I use my already known spells in my spell slots?
at my table the DM is going to determine what spells are known either completely at random or at random from a list of spells that he would have modrons cast anyway, and in the same manner for other outsider forms, but I doubt that my power level will exceed the incantatrix or artificer