Duskblade 20. Hexblade 20. Wizard 9/Fighter 1/Eldritch Knight 10. Wizard 5/Fighter 1/Eldritch Knight 9/Abjurant Champion 5. I'm not seeing the issue here... those are perfectly viable builds of varying power levels, and hardly an out there multiclass combo... just take a little of the base classes, and add in a hybrid PrC designed for the purpose, and you're there.
Note how the builds you offered with actual multiclassing both require PrCs? That's what I'm talking about. I think multiclassing could be viable without need of PrCing the crap out of it. Basically, I feel that the importance of PrCs should be a little diminished.
Why should that be balanced? You can make Fighter/Wizards after all. Not every possible iteration of every combination must be balanced... it's just that the strong ones shouldn't be overpowering, and you should be able to make a strong enough one for any given character concept. Fighter 10/Wizard 10 is just a bad combo, but if you want a Fighter/Wizard, Fighter 1/Wizard 9/Eldritch Knight 10 will give you that, so that's hardly an issue.
Because the player shouldn't
need to research a viable build to implement a concept. I'm assuming the average player has a good grasp of mechanics, but not enough that he's an above average CO. There are currently well over twenty splats out there; making a gish already requires one of them, and that's easily the first combo I can think a player would find awesome.
Again, can you name the sort of character concepts that will lag behind? Obviously making silly build choices will penalize you, but then again a Fighter 10/Wizard 10 is perfectly balanced against a Cleric 20 if the Cleric is as bad in making spell selections as the Fighter/Wizard is in build selection.
Mainly spellcasters, I believe. Some skillmonkey mixes, too, but that's more of an issue with how some classes have LUDICROUSLY low skill points.
Yeah, so your Rogue 5/Fighter 5/Ranger 5 gains an extra 5 bonus feats at the cost of two feats... I see a problem with this cunning plan. But really, I think the balance is currently slightly in favor of multiclass characters... single class characters are possible, but are often weaker. So pumping up multiclass characters seems to me like a plan that will remove single class characters as a viable option.
This was me mostly tossing ideas out there for critique. I'd say THAT objective was accomplished.
Why cost multiclassers a feat? They'll still be worse than full casters while the latter loads up on Metamagic and DMM.
Again, tossing ideas. As Jaron pointed out, right now the balance is slightly in favor of multiclassing, and I think a feat investment is a small price to pay.
If you do the common "add half of level to all classes up to maximum" variant (round down) you'd get a L15 (+7) 5/5/5/ character with abilities of Ro12/F12/Ra12.
Close, but that's 6 less class levels and 2 less than character level. If those were spellcaster classes rather than warrior/expert it means much more.
I forgot to mention that all the other class features they'd normally gain are lost. So, for example, our hypothetical construct wouldn't have Improved Uncanny Dodge, the level 10 rogue abilities, the ranger's advanced combat style, and the Fighter's bonus feats (assuming we create other class features for them).
Hardly a perfect idea, though, and your example sounds a bit more workable.