That's a weird statement from a designer. I myself find it great that they care about it. These symbols become part of the city's identity, I'd say that's pretty important.
Vastly more important is the proper purpose of the signage. It signals to someone unfamiliar with the surroundings there is an underground train station here. The targeted persons who require this signage and are helped most by it are predominantly not residents of the city and therefore have little reason to feel identity or affiliation.
Much like regulated traffic signs, it is better that cities do not design their own unique logos, but use a standardised one. See the paragraph on http://mic-ro.com/metro/metrologos.html starting with "Some logos are ubiquitous, at least nationwide" for places where cooperation won out over individuality.