I'm not sure, if ranking a player strictly on his ability at his specific position, rather than taking position into account, if guard Chance Warmack from Alabama isn't the best player available in the upcoming NFL Draft.
He will play at least a decade in the league. It would surprise no one if he is eventually an All-Pro.
The Lions do have a need at guard. Why not select him fifth overall?

Chance Warmack: Best NFL guard prospect

There are a number of reasons they should not. First and foremost is he's a guard.
The idea "take the best player available" regardless of position is not a wise one. Some positions are simply more important than others in the NFL Draft. Guard is near the bottom of the list, above fullback and kickers.
It's because guards play in limited space. There is a tackle and a center on each side protecting them. A tackle has to be agile enough protect an open border. It's why the best athletes on the offensive line generally play tackle. Secondly, a guard never touches the ball - like a skill position player on offense. He can help a team score touchdowns, but won't actually be the one who does. Unlike a center, a guard doesn't snap the ball and is rarely as involved as the center with the line calls. A guard's job, in simple terms, is too not be a weak link in the chain in the passing game and run block. It's not that it isn't an important spot. Poor guard play certainly doesn't help a team - and superior guard play does. But there are much more pressing concerns. It's an easier position to fill adequately in the NFL than most others because it doesn't require as much athleticism.
It's why no offensive guard has gone within the first 10 overall picks in the NFL Draft since Colorado's Chris Naeole in 1997 by New Orleans. He was a solid NFL starter for more than 10 years, but few people remember him. It's not his fault. It's the position. It's a limited impact position.