I'm not a fan of overpaying Williams, if the time arrives where he prices himself out then yes, we should let him go, the Ravens are certainly in the right to let him go at +10M. I'll be honest here, I wasn't a fan of prioritizing Williams over Wagner at first, but after seeing what happened to our run D late in the season, and seeing the regress of Timmy Jernigan, I felt that the defensive line could be in trouble without Williams next season. However, if I can keep Williams at a good price but have to let Wagner go as a result, then I would do it.
As far as Harrison's contract goes, that's the mark for the #1 run stopping NT in the league. I don't see any reason for Williams to surpass that by a high amount, the cap number will be going up, but I don't think that automatically means teams are going to just throw money at FAs.
In Wagner's case, the 10M per year seems way too high, I would be shocked if he got that amount. The only way I see Wagner getting 10M or even above is if a team expects that he plays LT that next season or in the least sees him just as versatile. The highest paid RT is Lane Johnson but the Eagles paid him with the expectation that he'll move to LT.
As far as the Ravens comparison between Alex Lewis and KO, I find that interesting because the Ravens didn't view KO as a LG exclusively, they viewed him as someone who can play all over the line, they just had someone who they signed long terms in Monroe, and Wagner who was holding it down at RT, beyond that the Ravens viewed KO as a potential option at LT and to a degree, it harmed them in the end because even the Oakland Raiders agreed to that. Of course you and I know this, but I think the Ravens comparison Lewis to KO could also speak to his versatility. We did see Lewis at LT, even if it wasn't pretty at least he played there. I think the Ravens not only think he's a really good LG, but they might feel that he's just as good at RT, that could convince them to grab a LG and have an even better line this year than last with C being the only spot they would have address via draft. You can do that, and in the process retain Brandon Williams if it comes at a good price.