I think the point is, and that you rightly make: If there is a way we can improve the Oline with proven veterans, that is a better option than drafting them for many reasons.
One, they have done it! Less risk.
Two, related to one, any drafty is a risk, no matter where they were picked--the NFL is ripe with examples of high draft picks at every position who turned out to no be worthy of their draft status.
Three, it allows you to go after other needs in the draft--and this could also be vise-versa, signing skill players and drafting lineman.
Four, lineman generally take longer to develop, so the impact of drafting them takes time, it takes patience, do the Bills and their fans have the patience?
Five, related to item four above, the one person who suffered the most for that online development time is the QB who is taking all the hits--can the Bills afford to pay that price with the new shiny toy at QB?
Thus, I like the idea, but we know getting them is not as simple as wanting them. Nonetheless, if it could happen, I think it is the best way to build the Oline; that is, mixing skilled and proven veteran signings with your own draftees who are developing.