A few things :
Balor has 75% damage reduction against sonic.
Epic mass Heal can't be picked by Arcane spellcasters.
4 - IGMS (2 x Quick (48d6), 2 x Maxed (288) = 455
8 - Sound Orb, 4 x Quick lssr (36d8), 4 x Maxed Norm Orb (576) = 743
6 - 3 x Quick lssr Sound (27d8), 3 x Maxed IGMS (432) = 648
4 - 2 x Quick Lsser Sound (18d8), 2 x Empow Orb of Sound (36d8) = 180
5 - Empower Orb of Sound (90d8) = 626
5 - 1 x lssr Orb Max (72) 4 x Empow Lser Orb Sound (36d8) = 322
= 2974 - 25% = 2230 damage in 19 rounds, following those 1 Assay Assistance and 6 rounds of avasculate.
That is 6+1+1+4+5+1+2+3+2+4+2+2+1 = 34 rounds, not 19 as far as I can tell.
Also there is the problem of dealing with Mordenkainen and you can miss a few RTAs when you cast that many.
So, without trading insults and just using the math, has my lack of knowledge produced a build that can summon, buff and defend, melee less/mid mods, then also nuke the Balor?
No, with such a spellbook you want to go straight to the balor and so would need to use ethereal to get here then manage to lure the Balor away from the other mobs. Meleeing your way through the top would take ages with low AB like that builds has, and you'll be breached and nuked.
1) The Bladesinger PrC can go one on one with the Balor and nuke it in under 3 minutes, maintaining strong defences.
No.
2) Bladesinger is the only purely arcane PrC that gives d8hp.
Uhm yes, so what ? You can go dragonslayer and get d10 hp.
3) Bladesinger is the only PrC (arcane or not) that has a stat based AC bonus (upto +5) that is KEPT in armour
Yes ... so what ? You can't have a shield.
4) Bladesinger is the only wiz/sorc PrC that can cast in armour, for free. (Saving 4 feats, 3 of them epic. Also doesn't need level 9 spells).
Picking the PRC is far from free.
5) Bladesinger is only caster PrC that can use one stat (INT in this case) for: Damage (+10, same as 30 str), AC (+5), spellcasting & bonus spells, all whilst wearing light armour (+6 AC).
Yes. Of course if you focus on INT that much your AB will suffer from it.
6) Bladesinger is the only PrC that can give a level 5/6/7 spellbook with plenty of spells to a strong melee base that casts in armour.
I'm sorry, what ? See all the divine casters, bards, warlocks, auto still mages.
Perfect for Weapon Master (Already has 4 of the 6 feats required)
If you want to have low CL sure, the tradeoff is questionable.
Perfect for Swashbuckler for Insight melee damage (+20 INT damage) with option for Epic Precision.
Epic precision for SB is at 12, once again we're in low CL area.
Perfect for assassin with bluff skill and free feint feat, plus high DC death attacks (with insight damage), and auto quicken spell avasulate via ability for that first round.
Already said how inferior that build was.
Regarding the :
A power PrC suggested by elf players, QC'd by elf players and Dev'd by elf players, for elf players.
I disagree it's a power PRC, also it wasn't QCed only by elf players. A good thing you mentioned shapechange though as I didn't think about it.