I think you may be right on first part. But theory that Lacy will be better in cold weather is baloney. Modern football fields (that would be anywhere but Soldier Field) have good footing year round. Lacy won't be any quicker in winter. That was 20 years ago when passing game shut down in bad weather, and big backs ground through the frozen ground and snow.
MM using just one back yesterday was ridiculous, particularly a guy who is struggling.