It's about adding depth not necessarily upgrading because, as you said, real upgrade are costly but some depth guys on the defensive and offensive lines could have been out there. We all know the offensive line issues and the D-line at edge is Hutch, a relatively unproven AQM and two bandaids, it wouldn't have hurt to bring in some insurance, can never have enough pass rushers.
With that said, there were no real options out there that truly move the needle so there's no need to be overly critical of Holmes. Ultimately the Lions have a very talented team capable of making a run and every team outside of maybe the Rams have some real question marks so it's all there for the taking for the Lions. I think the coaches need to scheme better. I think Morton has been very poor at adjusting, we saw no adjustments against the ultra aggressive Tampa and Minnesota defenses, just a bunch of Goff drop backs with no time to throw. He needs to be better as does Fraley with the blocking schemes up front.