That's fair as long as we agree that, at least in part, your evaluation is subjective. A rudimentary look at things like OPB says Turang is in the lower half of the league (relative to lead-off hitters) and most lead-off hitters with a lower OBP than his make up for it with a much better ability to produce runs. Very few produce a lower wxOBA than Turang. If he can't get out of this tailspin (which, as someone else noted, is far more than 20 games), it looks bleak.
The reality is that teams deploy all kinds of different hitters in the lead-off spots with all kinds of different profiles and skill sets and most teams use multiple hitters. Very few hit lead-off as regularly as Turang does and most that do are all-stars. Which is kind of the point. Teams use really good players in the lead-off spot more often than not and usually on of their better hitters.
There may not be a ton of options but there are options. Even if there were not, if every hitter is slumping why not shake it up and see what happens? Whats the worst that can happen? Turang hasn't proven nearly enough to just say "let him ride it out".