Actually, any time the DM calls for a check, that's DM Fiat. Likewise, anytime the DM sets a DC.Everything has a Check against a DC or creature's insight. 30 is nearly impossible, as you see in the player's book.
All the prep your sorcerer has done: That's DM Fiat (especially as you perpetually refuse to allow any other character anything like that much prep). I'd say that's more of a DM fiat than the poster above who had his cleric use Divine Intervention to replicate a cleric spell (plane shift, since the guidance for the class ability specifically says any cleric spell is appropriate.
You want a real 1 v 1 fight? Start the characters with no spells up. Put them in a cage, just the two of them--no minions no allies. I'd strongly recommend banning wish and simulacrum in this circumstance--and I'd be willing to allow the sorcerer to take a replacement spell for it. Heck, if I were feeling nice, I'd allow you to have the hit points back instead of the magen. If we wanted to be rigorous, we should run it a few times.
But that's not what you want. You want something else. You want to use your sorcerer to out-wizard wizards, and ... that is at least not playing to the sorcerer's strengths--and it's very much playing to the wizards'. Your sorcerer is setting up a checkerboard while the wizards are playing Go.
That. That is why we are all laughing at you.