I agree with your assessment of Luke, but he's still a talented grappler, and also has a significant size advantage.
Anyways, excellent breakdown of the matchup. I agree that the entry will be the key for Islam. His striking offense may be more pedestrian than Oliveira's, but his striking defense, head movement, and the timing of his TDs are all much more sound. He has a decided advantage over Charles in those areas. I think he'll have a relatively easy time getting takedowns because of this, and once he's on top, with that physical strength, heavy top pressure, and his overall level of grappling prowess, it won't matter how good your BJJ is.