glass
(he, him)
Nobody can "cast a spell slot" because that is nonsense.A 3e Wizard can use spell points to cast a spell slot. A 3e Psion can too.
A 3e wizard uses spell slots to cast spells. Points do not enter into it.
A 3e psion uses points to manifest powers. Slots (or spells for that matter) do not enter into it.
A 3e psion does not have a spell list at all, it has a power list. Some (nowhere near most) powers have similar or identical names to spells, and may work similarly, but not identically because they are not spells.The spell lists of the 3e Wizard and the 3e Psion are nonidentical but mostly share the same spells.
5e wizards (etc) are not spontaneous, they use a non-vancian form of preparation (Monte Cook called it readying in Arcana Unearthed, but sdaly that terminology did not catch on both Paizo for the PF1 arcanist and WotC for 5e chose to overload the term "prepare").Spontaneous spell casting is new for the 5e Wizard, but is normal for the 3e Psion.
TLDR: In the immortal words of Luke Skywalker, "Amazing. Every word of what you just said was wrong."
_
glass.