‘Niche’ is relative to the campaign. In a Three Musketeers style campaign, where slaying nobles will get you ‘High Justice’, (and not in the good Cheech and Chong way), non lethal options may be greatly appreciated, especially when fighting Evil Count Tyrone Rugon.
Is this ‘Niche’?......probably in the grand scheme of all games.
My personal experience is all campaigns have idiosyncratic elements that encourage ‘niche’ play.
If Character optimization is important to one, then a Warlock is going to be played only one way.
A player that decides to Min/Max more unusual options then “EB Pew-Pewness”, has more to work with in the Sorcerer class. That is my opinion at least.