The other angle you could go with is using ML as a stock option. Buy him now and I am sure the only news we will get for a year is how amazing his comeback is and how he is confounding all the doctors with his incredible healing powers ,then turn around and trade him for a lot more than you paid for him this season (assuming you can hold him on your roster).
I'd say the same for Michael. Look at the value bump that David Wilson and Lamar Miller got when the path cleared. That will happen for Michael too.
He's stinking up the joint right now against Oakland, but as a whole he has had a great preseason. Positive buzz right from the start carrying over to production in the games.
I think one of the skills that can be valuable in dynasty is the ability to spot the guys who are going to pop right before everyone else catches on. Like Demaryius Thomas, CJ Spiller, LeSean McCoy, and Jimmy Graham. There was a time when those players weren't untouchable. It's a stretch to put Michael on that level right now, but he has the feel of a guy headed for that trajectory. I think he's a player where people will be looking back in another couple years wondering why they didn't pounce when he wasn't untouchable.
I think people are being way too optimistic about Lattimore. Two severe knee injuries in two years. He was basically a flyer by the 49ers. The idea that he's: A.) going to get back to his old 100% B.) have an easy path to a starting role and C.) actually stay healthy requires a huge leap of faith. I think it's a smaller leap with Michael. All of the signs point towards him being a legit talent. The main variable is opportunity. I think that's a "when" rather than an "if."
I generally advocate the longview in dynasty and I don't see that equation favoring Lattimore over Michael based on what we know today. It's one thing if you take a guy like Gio who has a real chance to produce this year, but Lattimore will be on the sidelines all season and in the same position a year from now that Michael is in today. A rookie looking to prove himself and carve out a role.