We really don't know what's going to happen. Just because something happened before, doesn't mean it's going to happen this year. The lines don't have memories, just like the roulette ball doesn't have a memory. Sure, the linesmakers can adjust, but maybe in the short term (rest of this year?) fav's will STILL beat the line! I have some dogs this week in NFL and I know that 58% can't hold up FOREVER. But, I really have no clue how long it will hold up. Maybe 4 more weeks, maybe the rest of the season, maybe midway through next season. If we knew the answer to when fav's would stop covering at this rate, we'd be able to make some money by betting all fav's up to that point.
What I'm saying is, yes...linesmakers can adjust and that's why fav's covered less than 50% during those 8 years you are talking about, but who knows.....there is a first time for everything. At the beginning of the season, if someone had told me that fav's would cover at 58% all season long, I'd say "wow, that's crazy", but since we're more than 1/2 way through and they're already at that number, it wouldn't be totally out of the question.