For a couple reasons. First because bringing a vet LG in improves our depth by making Jackson or Boom (whoever is not penciled in as LT) available as a swing tackle. Secondly because they are cheap relatively speaking and the Rams don't have all that much invested in the OL. Boom's contract is below what the top LTs will be paid and Hav's contract is very team friendly.
So if the Rams agree with you re: their board, which would not surprise me btw, then it fits that they prioritize Edge with that round 2 pick and then take a C at some point when things line up thereafter.
At least I presume they will draft C. Simply because good ones don't tend to hit FA. Generally you gotta draft those guys and you can get them outside the early picks. Only concern I have from there for the OL is LT. Simply because I don't trust Boom or Jackson to stay healthy. But I agree round one is the way to address it, just worries me that our QBs might be sweating their blindside again in 2023.