I dont necessarily disagree with you but you need to keep in mind the circumstances which the Ravens were facing - they were about to release Boldin, who as Vinny mentioned refused to restructure his contract, anyway and would have risked seeing him go to the Pats or Colts or Texans even.
The Ravens may not have gotten much with that 6th round pick but they freed up some much needed cap space, as well as made sure he didn't got to another AFC team. Also, not many options there for trade partners when talking about a 33 yo WR (about to be anyway), who was due 6-7 mil in salary (also due to cap space limitation many teams out there are facing), which limited what they could get in a trade.
Plus, as Vinny mentioned again, Boldin may have been great in the p-offs but he performed well above his average/usual level there, so can't just freely assume next year you'd be getting the same WR, who was instrumental in the Ravens' SB run this postseason ... not at that level, at least.
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a comment on the ESPN article about the Boldin trade: