Short version: Most of the similarities are visual as Lion King was a homage to Kimba. I do not entirely believe the artists actually were familiar with Jungle Emperor. Similarities with plot are superficial at most. Like saying that Ribsy and White Fang are the same story because they are both about dogs (or is it Call of the Wild that's about a dog--I hardly remember now). Animation parallels abound, connections to Tezuka's themes do not.
Long version: I don't really feel a need to consult outside sources when having my own opinion--and while that comes off as rather sassy, I'll stand to any free thinker keeping their opinions just that.
That said, there ARE certainly similarities, but it seem far too easy to get caught up in the similarities that are superficial and miss the gross dissimilarities between the two works.
The Lion King is first and foremost an adaptation of Shakespeare, and while we can whine and moan as much as we want to, it bares nothing more than a superficial similarity to Jungle Emperor. It you want, I can digress along this topic at length, but suffice it be said that Lion King is very much a simplistic 'reclaim your own kingdom' sort of tale, with a bit of 'coming of age' story thrown in to the mix.
Jungle Emperor however is something very much different. Here we have a sense of unfinished destiny, interdependence, the entire circle of life (not the rubbish Disney was singing about) and also the very early form of what would become the phoenix premise--namely, that societies will over time evolve, and we can imagine them evolving toward a higher, even more spiritual goal. It of course comes about that it is very likely such societies will self destruct, or the base instincts which we all possess will lead us to ruin, leaving society itself in decay.
To suggest these themes--those which make up the very corner stone of Leo--are present in Lion King, is purely rubbish. Superficially (and artistically) the connection is very real; but I am afraid the story telling department has fallen far shy of then intended target and instead we have Shakespeare with lions (not a bad thing after all, really.)
If you'd rather take Fred's view on it, you are certainly more than welcome. He is an expert after all, and I don't doubt that he has some insight I haven't gleaned from reading and viewing all the episodes. That said, he must be a very good reader if he sees proto-phoenix in The Lion King, and I dare say that no amount of writing on his part will ever convince me that such a thing is actually present in what is in all counts a fairly mainstream movie that does not, in a single moment of its celluloid existence cause me to think or question or even feel alive in the same way that Jungle Emperor does.
Rather I'd say that Lion King is little more than commercial fodder, and while people are (correctly) right to point out the homage, they are absolutely incorrect in stating that Lion King is a reiteration of the themes present in Jungle Emperor. I would strongly recommend that by whatever means necessary, people actually go about reading Jungle Emperor. Here is where the evidence lies; here is where we find the sad joke about Lion King being a remake of Jungle Emperor.
I look forward to reading what Fred has to say, but I suspect, as I found in most of my research, that the parallels lie in animation, not in story telling. That said, despite my sassing off, I both look forward to and dread being shown wrong by Fred's essays. Look forward to because I enjoy the intellectual stimulation, but dread because if the case can actually be made that Lion King is a remake of Jungle Emperor, it must certainly be one of the worst adaptations of all time.