I played it because I found it to be the most enjoyable of the three options. A number of people I had met in game also felt the same. But of course this information would be difficult to determine without polling done at the time. Despite paladin being an actual hindrence in 3.x in many circumstances, people still ran it and played it. Despite not being meta it saw a similar play rate, but not a similar clear rate pointing to the need for adjustments of some sort. Contrast with now, Dark Knight is capable of clearing content, but is being run less than half of the expected rate.
There is no reason it wouldn't be considered fair. This point must be justified. Despite paladin being almost certainly the lesser of the two options in HW its funny that looking at the play rate people played paladin at a rate which would be considered similar to dark knights. Despite paladin's status in 3.x people still played it based on pick rate. Contrast to the situation now, Dark Knight is certain viable in every sense of the word, yet people aren't playing.
Play rate didn't mean paladin didn't need adjustments, but it does mean that people enjoyed the playstyle which was, by and large, untouched in 4.x. We saw some adjustments to our dot, and a small adjustment to our rotation to take enmity out of the equation, but nothing really changed. Block now blocks magic, cover reduces damage, casts are no longer interrupted on a tank who gets hit for a living, all changes which were necessary but no massive changes to our rotation other than adding a second burst window which thematically fit with the class.
Certainty isn't where I would set the bar on most things outside of mathematics. Nothing is certain. However, if reprisal were still a dark knight exclusive, had an int debuff, had its animations restored, as well as gaining its stormblood abilities, and having the QoL adjustments that we have waited 3 years for, along with the kit adjustments we've seen this expansion, and as well as other improvements the community is still waiting on... Then yeah I would be pretty happy to play dark knight again and I think most people would enjoy the class more.