Except they confirmed we're defeating the Legion IN Legion... so...
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Yes we are getting another raid tier what lol. Do you even watch Blizzcons? At Blizzcon they have stated that 7.3 brings us to Argus, there WILL be another raid and it WILL be on Argus, and they have stated that the Legion is getting defeated in the current expansion. They've also stated multiple times on dev Q&As that there will be a raid tier on Argus during 7.3 or 7.3.5, not the next expansion.
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They have but anybody who goes that way gets lost to the sea... so... there is technically no confirmation that there isn't something.