According to James Jacobs ( http://paizo.com/paizo/messageboards/paizoPublishing/pathfinder/pathfinderR PG/general/archives/whatIsSoOverpoweredInNonCore3XEditionThatItRequiresAMaj orPowerBoost )
"most of the later base classes (duskblade etc.) were more powerful than the core class equivalents"
This is simply not true. The bulk of non-Core classes are weaker than the most similar Core class and most of the rest are balanced. In addition, in most of the cases in which a non-Core class is more powerful than the closest comparable Core class, the Core class in question is one of the weaker Core classes.
I know that there are other reasons for boosting the power of the Core classes (reasons that I don't particularly like) but if any part of the reason for boosting the Core classes is that they are weaker than the non-core classes, then I'm pretty perplexed.
Because of the pretty much across the board boost in power to the Core classes in Pathfinder a lot of 3.5ed non-Core classes that could otherwise be easily ported over instead end up looking pretty damn gimpy. I think this is an example of weakening backwards compatibility without doing anything to improve play experience (if I want more powerful characters, can't I just start everyone one level higher?).
Let's go down the list of non core classes (I'm sure I'm missing a few, but this is the bulk of them):
1. Archivist
Closest core class equivalent: cleric
Power level: balanced (both are very powerful)
2. Artificer
Closest core class equivalent: wizard
Power level: balanced (both are very powerful)
3. Beguiler
Closest core class equivalent: rogue/sorcerer multi-class.
Power level: more powerful
5. Crusader
Closest core class equivalent: paladin
Power level: more powerful
6. Duskblade
Closest core class equivalent: gish multiclass
Power level: less powerful than a purely core eldrich knight(self-buffs are what gives gish their power)
7. Dragon Shaman
Closest core class equivalent: bard
Power level: less powerful (bard spell casting is fairly powerful)
8. Factotum
Closest core class equivalent: rogue
Power level: balanced (different focus, hard to compare)
9. Favored Soul
Closest core class equivalent: cleric
Power level: less powerful
10. Healer
Closest core class equivalent: cleric
Power level: less powerful (focus too narrow)
11. Hexblade
Closest core class equivalent: gish multiclass
Power level: much much much less powerful
12. Knight
Closest core class equivalent: fighter or paladin
Power level: balanced (different focus, hard to compare)
13. Marshall
Closest core class equivalent: bard
Power level: less powerful (except for one level dips for the Art of War ability)
14. Ninja
Closest core class equivalent: rogue
Power level: less powerful (MAD and weaker damage mechanic)
15. Samuri
Closest core class equivalent: fighter
Power level: less powerful (do I even have to explain?)
16. Scout
Closest core class equivalent: rogue
Power level: less powerful (generally ends up dealing fewer dice of damage)
17.Spellthief
Closest core class equivalent: rogue/wizard multiclass
Power level: less powerful (assuming the rogue/wizard multi-class has some sort of PrC) they're very very narrow focus gimps them horrifically.
18. Spirit shaman
Closest core class equivalent: druid
Power level: less powerful
19. Swashbuckler
Closest core class equivalent: fighter/rogue multiclass
Power level: less powerful
20. Swordsage
Closest core class equivalent: monk
Power level: more powerful
21. Warblade
Closest core class equivalent: fighter
Power level: more powerful
22. Warlcok
Closest core class equivalent: sorcerer
Power level: less powerful (being able to have weak powers all day long doesn't stack up too well with having fewer strong powers)
23. Warmage
Closest core class equivalent: sorcerer
Power level: less powerful (direct damage is a sub par for casters)
Note I am not familiar enough with Incarnum, the Dread Necromancer, the Tome of Magic or Complete Psionics classes to include them, but I've never hear anything about them being especially powerful. As far as Tome of Magic goes specifically, I've heard that all the classes in there are significantly weaker than core casters (especially the poor poor broken Truenamer). So if I did know enough to be able to count these it would make non-Core come out even weaker.
As far as the four basic psionics classes I kind of think of them as core because they're in the SRD, but if you want to include them then the Psion and the Wilder are balanced with the Wizard and the Sorcerer respectively, the psychic warrior is more powerful than a fighter and the soul blade is arguably weaker than some NPC classes and is badly-designed joke of a class (much like the monk in Core). Overall the XPH has about the same power level as core
Tally
More powerful: 4 (note all except for one of these classes are from the Tome of Battle, basically 3/4 of all classes that are more powerful than their closest core equivalents are from a single supplement)
Balanced: 4
Less powerful: 15
This is not to say that using a big stack of splatbooks doesn't generally make a character more powerful, but that's more to do with people being able to cherry pick from a long long list of spells, feats and PrCs except for the Tome of Battle there was been virtually zero power creep with regards to non-Core classes. Because of this, boosting the power of the core classes is a very bad solution to power creep and would only make the problem worse.
The upshot of all of this:
A. If I play Pathfinder is makes it much harder for me to play fun classes like the hexblade, warlock and scout which are fun to play but weak compared to Core to begin with.
B. It makes we question just how well the Pathfinder team understands how 3.5ed mechanics work.
