There are only 25 guys in the country who are paid 7 figures and the bulk of them have far more experience that Lea.
Lea probably isn't, but don't forget, this is Lea's first Coordinator role so I wouldn't expect him to have been making 7 figures when he first got the job. Rees is paid appropriately to his resume like anyone early in his career. but he is nowhere near 7 figures, nor should be be. In fact, he probably won't even get there in his next contract, nor should he.
You can do your own research. Just look at the USA Today list. Most of the guys who are making big bucks have lots of experience. Good comparison to Lea is Jim Leonhard (same age by the way) at Wisconsin who just got raised to 960K in his 4th year as DC. 2021 will be Lea's 4th year. Heck, Bud Foster who is one of the best DC's in the country at VATech is only making 1.0M.
Elko was paid in the top 10 of all college assistants before he left. The offer on the table from ND at the time would have made him basically the 5th highest paid assistant coach in the country.