alt Hacker News100%.
Ignoring the fact that sometimes founders feel the need to put their stamp on everything, for startups and scaleups that haven't progressed to corporate slog, I think it's near impossible for even the best staff designer in the world to arrive at the optimum website/deck/infographic/widget without founder or leader feedback.
The key ingredient is their insight. That's what sets any startup apart. Otherwise the designer would be the founder.
Sounds like the founder as well as the customers are who the designer should be gathering data points from.
I think anything where a surprise is presented (in design or otherwise) means some missed communication.