Good god...this kind of debate again.
If you subscribe to what Mike, Dan and others were talking about then maybe the reason why most people never are able to use Aikido successfully is because the "core" skills are just simply not being taught
I think there are two 'core' concepts here actually. What judo can offer is a lesson in the core principles of kuzushi, tsukuri, kake. What judo offered nihon jujutsu was a pared down set of throws that got at the heart of what made for a good jujutsu throw. Once you learned those lessons, approaching the specifics of a particular line of jujutsu became much easier because you could understand why the pieces of a technique were done the way they were. I think a lot of jujutsu ryuha also took the lessons they learned in judo and applied them back into their arts however, so you see a lot of meiji era jujutsu that looks very judo-y. Even some older ryuha incorporated these principles back into their arts.
The other set of 'core' teachings you bring up would be the internal dynamics/skills. You watch videos of Mifune, and you realize that some of these guys had it, but others just developed enough musculature to be able to throw without it. I would imagine that Kano's love of Western education probably didn't do many of the more esoteric training methodologies any good, as they probably didn't fit into the PE training paradigm he was shooting for. I could be wrong however, if you look at the Kosen Judo guys, they sure do some weird stuff as solo and paired exercises. I'm sure a lot of them approach it just like lifting weights, but many of them could be done with the eyes turned inwards as interesting internal training tools. It could also just be gay pr0n, but I digress... (Anyone whose seen the exercises in question will get the joke there.)
If you're able to find a teacher and dojo that get both sides of that however, you're going to be getting some very good stuff (a la Mifune...). I don't believe it's enough to just know what's going on inside, particularly for a jujutsu art (which I consider aikido and judo to be subsets of). I think it would be easier to transition from non-applied internal practitioner to practical fighter with the striking arts. With grappling/throwing arts however there is an almost equal need to understand the principles of the interaction in order to understand how to apply those internal/baseline skills. For example, I feel kuzushi is just as important in aikido waza as judo waza. You may get kuzushi differntly (or not) but it is just as critical. Aikido without kuzushi is just kansetsuwaza and not really different from any other form of jujutsu *whose goal is to injure the joints of the attacker*. Applying internal power/fa jing/ mad ki-blast skillz to an improperly done joint throw will only result in damage to the joint and injury. This, I believe, is outside the framework for aikido, and yet, it's how most people do their waza.
Unfortunately, I don't see either sets of what I consider to be core skillsets/principles being taught much in aikido anymore.