Joe D is taking a long term approach to the OL building. He's not dumb, he knows that the OL, usually, is built in the draft.
In FA he's going after versatile, disciplined players that fit the scheme as stop gap options. They aren't building blocks but players that can hold the fort until he can properly rebuild the OL.
Fant is athletic and a potential revelation if there coaches can harness his potential. His glorified 1 year contract pretty much reflects that.
McGovern is young and good enough to be someone that can be a constant presence on the OL for the next 5ish years.
Van Roten is a depth signing, that once again is a scheme fit with good game tape.
I think we take 2-3 OL in the draft, personally. There are potential day one starters that will be available in rounds 1-3. I think Joe is doing a solid and sensible job so far in rebuilding the line. It was never going to be a quick fix.