Unreal Tournament 4 didn't get a chance to fail because it was never a real release. UT4 was a free tech demo for Unreal Engine 4 that never got completed because Fortnite started taking off at that time and developers were deallocated from it.
And UT3 was definitely not a great game by anyone's measure.
It was never officially released, but it was on the front page of epic launcher for years, even after fortnite took off. The online experience was fairly complete and enjoyable (for people with experience) for ctf, duel, tdm, and team arena master. But yeah, epic didn't support it as much as they could have.
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The people behind UT were reallocated to make Battle Royale mode for Fortnite which is the reason of the take off, not vice versa.