Which is, yes, a different thing than arguing about whether it's "a good idea" for society or innovation or whatever. The EFF summary focuses on the "good idea" thing, but the actual amicus brief addresses both -- although I bet you can find even more of the legal arguments in the first party brief.
From the amicus brief, take a look at the original brief, starting on numbered page 4, "I. The Federal Circuit’s Decision Has Disrupted Decades of Settled Expectations That APIs Are Not Copyrightable"
> That assumption was well-founded. It was based, in large part, on this Court’s own recognition, in 1996, that menu hierarchies that control functional capabilities are a method of operation, and thus uncopyrightable under 17 U.S.C. § 102(b). Lotus Dev. Corp. v. Borland Int’l, Inc., 49 F.3d 807, 815 (1st Cir. 1995), aff’d by an equally divided Court, 516 U.S. 233 (1996). Programmers and developers relied on that ruling for the proposition that APIs, like the menu hierarchy in Lotus, may not be copyrighted under § 102(b). Ninth Circuit law—which should have been controlling in this case—was the same: the “functional requirements for compatibility” between computer programs “are not protected by copyright.” Sega Enters., Ltd., v. Accolade, Inc., 977 F.2d 1510, 1522 (9th Cir. 1992); see alsoSony Computer Ent’mt, Inc. v. Connectix Corp., 203 F.3d 596, 599–600 (9th Cir. 2000) (describing Sony’s PlayStation BIOS as a “system interface procedure[]” that Connectix was entitled to reimplement under § 102(b)).