I'm not claiming that the alignment that New England showed wasn't their goal line run defense...'only' it looks thin to me.

This has already been posted:

Before that final 2nd and goal and attempted pick play. DB Malcolm Butler was on the Patriot sideline. He wasn't going to be used as a defender.

When it was observed that Seattle had three WR's in their huddle. Malcolm Butler was sent into defend on Settle's RHS along with and set up behind CB Brandon Browner who was assigned to cover Seattle WR Jermaine Kearse. Malcolm Butler had to cover Ricardo Lockette. The plan was for Browner to force Seattle's Kearse back and into the path of any Seattle slant play with Ricardo Lockette as the target.