It wasn't 3 guards. It was 1 OG (Mafi), 1 OC/OG (Andrews), and 1 OG/OT (Sow). Claiming that they weren't needed is ignorance at it's finest. YTou talk about Onwenu, but ignore the fact that he's a UFA at the end of the year. You also have no idea if the Pats have tried to re-sign him already and whether or not Onwenu rebuffed them.
The Only Reserve IOL the Patriots had prior to the draft were Ferentz, Russey, Murray and Hines. Thinking that they couldn't be upgraded speaks volumes about your inability to evaluate the talent on the team. Andrews allows the team to part ways with Ferentz, who is 34. Sow or Mafi would allow the team to part ways with Murray, who is undersized. The 3 will also push Russey and Hines to improve or be cut.
Your "grades" don't mean a thing especially when you're working from a such an uninformed position. No one cares what you wanted. It doesn't matter one iota. Not to mention that throwing out grades when the players haven't played a down is just ridiculous. What matters is where the team saw players in relation to what they already had. People like yourself always complain as if you've got some MASTER INSIGHT into the future.
We don't need an Antonio Brown on the field. We need players who get open and make catches without fumbling. Boutte and Douglas are low risk / high reward players. Douglas is closer to being an "Edelman clone", just faster. Personally, I'd settle for a Troy Brown clone. And Douglas looks to be a faster version of Troy Brown.
If Boutte's ankle is finally 100% and he has confidence in it and he can learn the play-book, he could be a deadlier version of David Givens with a ceiling of Deandre Hopkins or Jordy Nelson.