> [T]here was never some grand conspiracy by Microsoft to create a format that competitors will find it hard to implement.

No, it's just an ordinary conspiracy. Everywhere in the spec you see shit that says "Do it like Word95 does" or "Do it like Word97 does" is an intentional aspect of the standard that makes it unreasonably difficult for anyone who wishes to faithfully read or write documents in this format to do so.

It is inappropriate for an open standard to define behavior in terms of an undocumented proprietary black box. The primary reason for an open standard to exist is to permit interoperability. Anyone who has read nontrivial portions the standard would argue that ISO shouldn't have standardized OOXML as it was. It's a damn shame that Microsoft acted in bad faith to exploit ISO's rules [0] in order to ram a very poorly-specified standard through. It's always sad when people and organizations that should be acting pro-socially choose to do the opposite.

[0] By paying money to stack the organization with a bunch of entities whose only interest was to vote "yes" for the ratification of this standard, natch. IIRC, ISO had to modify their rules again after the OOXML vote because they couldn't get quorum due to those one-issue voters refusing to show up for future business.