I think projections are weighting his past performance a bit favourably rn, there's a strong chance he's a below average hitter and fielder with no position and a fatal flaw in his swing that wasn't really exploited until late last season.
I have to say I would gladly part with Biggio as the primary piece in a deal for Bryant + Hendricks + Kimbrel, rentals be damned. I do not think Biggio is ever going to be the 3+ WAR player we thought he could be.