This framing is a bit hyperbolic. Saying Glaser was even the most influential art director of that era feels tenuous. But does anyone seriously think that a tourism ad campaign saved New York, or that a poster is what made Bob Dylan famous? Obviously good design is important. But also it's just a small part of a much wider world. When I see these kind of hero worship pieces I think of the coworkers that I have had to work with who have a massively inflated sense of proportion and genuinely buy this line of thinking. A bit of humility might be in order here.