The fact they locked achievements behind the DLC that shouldn't have been is about the only leg consumers have. This has resulted in lots of refunds, but doubt anything legally will happen.
Bungie will just say it was an accidental occurrence and patch a fix to get them outta the hot water
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Consumers have a leg to stand on in that they can demand better, but a lawsuit would NEVER succeed.
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Exactly Courts would just say "bungie is making an attempt to fix the issue" and throw it out. Sucks