Holmes needs to improve the quality dept on the offensive line this off season
Not that he can't try to do a little more this offseason, but I feel like he did a pretty good job addressing O-line depth this past offseason. How many teams have solid backups on the O-line? Don't forget the Lions also have a ton of money tied up in Decker, Ragnow and Vaitai, and will also need to pay Jackson and Sewell at some point. They still went and got Glasgow and drafted Sorsdal. Not sure what else you can do without throwing tons of money at backups who want to be starting.
Most teams don’t have 5 NFL quality starters. Lions have 6.
And O-line is the one position group in football where you don't do a rotation depending on situation, game script, etc. Injuries do happen but it's tough investing resources into players you hope you'll never need when there are other positions (like DL) where you might rotate in 7-8 guys every game.