I'm failing to see why anyone would pick a Sorcerer over an Erudite by the sheer comparison that one of them may be a little bit more powerful but the other is more versatile in every imaginable way. I mean if we went up to players who knew perhaps a minimal amount of optimization I believe they'd go for the guy who can do the other guy's job and do a psion's job as well.
Okay, let's assume the Erudite doesn't have infinite Power points because the Sorcerer can do that too, as below, and no retraining, because again, Sorcerers have all spells on their list known under that rule.
You have an Erudite with Spell to power. Compared to a Sorcerer.
Level 1-10, The Erudite sucks, because he can't even cast Arcane Fusion. Sorcerer has more spells that he can cast in a day, and they are better and more diverse. He also has the ability to be a damage class without sucking, if that's important. He also gets access to good spells a level before the Erudite. He also doesn't have to spend XP to get spells.
Level 11: Arcane Fusion. He has a shitty level 6 power he's not going to use, but he wins at level 1-4 and 6. Clear win.
Level 12:
Erudite wins level 1-4 in versatility wars, has the same number of level 5 and 6 spells. But worse level 6 ones. XP.
Level 13:
Erudite has more spells known of levels 0-4. He can use all his unique powers as level 5 and 6 and 7 powers, but his level 7 powers Aren't very good. He must spend XP for good level 5 and 6 powers now.
level 14:
Sorcerer now has level 7 spell that is better than whatever the Erudite is casting. Still has just as good and about as many spells of level 5 and 6, he also has all the good 1-4 spells, so maybe once or twice a day the Erudite pulls out something cool. The rest of the time, the Sorcerer is better.
Level 15-16: Repeat levels 13 and 14, except the range of spells that the Sorcerer is better at is larger, it's now 4 spell levels, that he has more spells known, to counteract the 4 spell levels the Erudite has on him. Except his are all higher level.
Level 17: Greater Arcane Fusion. Now the Sorcerer has better 8th level spells, but no 9th, and the Erudite is better at 7 and below. First clear win for the Erudite since level 11.
Level 18-20: Sorcerer may have worse level 1-7 versatility, but he counters that with much better level 9 spells.
And that's not counting the PrC advantage or feats or anything.
The Erudite straight loses levels 1-10 without even comparing favorably to Tier 3 classes, then he finally gets to be a real class, except he's always a level behind the Sorcerer in good spells (which is a travesty since the Sorcerer is already behind).
I was nice here, if I made the Sorcerer a Kobold, the Erudite loses both his clear wins to murky maybes and is clearly losing every level except 11 and 17.
The question is: Which occurs more often as a level 14 spellcaster:
"Man I really wish I could cast Knock right now."
"I only have Decerebrate and Insanity. I sure wish I had Avasculate or Stun Ray."
EDIT: You are also choosing to be a class that get's good spells a level later and spends large amounts of XP to even know those spells. You are going to be 2 levels from getting Fleshshiver when a shitty Sorcerer suffering from Skip Williams disease get's it. 3 Levels away when a Kobold Sorcerer does.
How? Prove it.
Sorcerer is in combat at level 12, he blew a feat on Arcane Disciple because this trick is so good. He blows all his level 6 slots. He then uses a level 5 slot to Planeshift to a Timeless plane where he rests for 8 hours, then gets his spells back, he uses a level 5 slot to Plane shift back, then he teleports if/when he needs to. 3 seconds after his disappearance he reappears with a full complement of level 6 spells. He repeats this as necessary.