Great guide... Note that I am not experienced with Level 1 Twinks but, based on reading the guide & reflecting, were I to rate the relative power deficiency of non-GrandFathered (nGF) level 1 Twinks to Lv1 Twinks with GF Specializations I would think off the cuff:
Lv 1 Warriors get HUGE benefits via Arms spec as they should be the best Tanks with 20% damage reduction in Defensive Stance, can deal more damage than non-spec'ed Warriors & can likely hit 2 targets simultaneously with 100% of their Slams if they build up their Rage and then dump it all with repeated slams while Sweeping Strikes is active...
Lv 1 Priests get LARGE benefits via Discipline spec as they are the only Lv1 Twinks who can Heal someone else & get Shadowfiend though they do less damage with their Smites... Priests are also the only Lv1s who can raise a fallen character though it may be that non-spec'ed Priests can also do that...
Lv 1 Druids get Large benefits via Balance spec as they get free Starfire which does 10 yard radius AoE damage & powers periodic Starsurges for extra burst & all cost NO mana...
Lv 1 Shaman get Large benefits via Elemental Spec as they pickup Lava Burst & Chain Lightning. Shaman are also the only Lv1s with built in speed via Ghost Wolf.
Lv 1 Monks get Large benefits from Windwalker spec as they can dual wield & hit both harder and more frequently & also generate chi to power Rising Sun Kicks...
Lv 1 Rogues get Large benefits via Assassiation spec as they have 20 extra Energy & hit harder with their Sinister Strikes & can use Shiv to cancel mob Enrages & maybe apply posion (if they can get posion)...
Lv 1 Paladins get Large benefit via Retribution spec as, while they do less damage from Crusader Strike they pick up an execute via Hammer of Wrath & get Blessing of Freedom & both Retribution Aura and Crusader Aura.
Lv 1 Hunters get Large benefit via Beast Mastry spec as they get a pet & can issue the Kill Command which causes the pet to get to & damage the target really fast. They and their pet also get self-healing via Leech for 10% of the damage they do via Predator's Thirst.
Lv 1 Warlocks get NO benefit from Affliction spec.
Lv 1 Mages get negative benefit from a DPS perspective though they do pick up Ice Barrier for a self shield so maybe it is a wash...
Pretty crazy stuff... Makes me want to create a bunch of levels 1s just in case there are more/future changes ;-)