Like with many of Tezuka's works, one of the most important themes in "Jungle Emperor" is the interaction between animals and humans. Kimba's parents died because of humans, but on the other hand he also met some friendly people who helped him, so he didn't end up hating the mankind. He wanted to learn new things from humans and bring the stuff he learned back into the jungle (such as agriculture or written/spoken language). He took on a habit of wearing clothes at one point, and he sometimes walked in a bipedal fashion. At the end of the story, he gives his life to save a man.
These themes are nonexistent in Lion King.
People usually post screenshots of a villainous lion with a scar. This lion looks similar to Scar, but his role is rather minor in the big picture. He's just some antagonistic lion who appears very briefly; nowhere near being the big bad of the story.
I've read the manga and seen the 1997 movie, but haven't seen the original cartoon series yet. I'm not sure if that series expanded on the scarred lion's role. Some of the clips from the series make it look like his fight choreography with Kimba was suspiciously similar to the end climax of TLK.
Kimba and Lion King are very different, aside from the basic imagery of "the king of the jungle" and common African animals. But Kimba does have some moments that look oddly similar to TLK; the scarred enemy lion, and mourning a dead parent who appears in the sky.
I think it's possible TLK started out as an adaptation with a focus on certain scenes instead of Kimba's entire life, but there was some problem getting the rights so they turned it into an original story instead.