I just know that any reasonable extension for BB6 will have me anxious about the eventual drop off. It would be tough having a slow skating non-play-driving winger on the decline locked in at $7-8m for (what is likely to be) very long term. Cup contenders usually don't have too many bad contracts, even one of those can be a big/costly problem. Like most UFA contracts, all we can hope is that we get at least 3-4 "good" seasons out of him. I would really hate to have buyers remorse immediately (kind of like the Eriksson/Stamkos/Lucic type deals).
I think a team can still be competitive with strong centers, defense and goaltending, winger is the lowest on my priority list. Even if we can't replace Boeser completely, I still rather let him walk than to commit something like $8m x 8, feels like the same bullet we dodged with Lindholm (who also only really had 1 offensively great season in his career, much like Brock).