Good design always matters, no matter what you are building, your timeframe or your goals. The problem is you equate good design with being perfect or precious, which in my opinion is flawed. Yes it is vital that you get your product out as soon as possible and claim the coveted title of being first to market (if it is a truly unique idea) and quickly get feedback so you can iterate etc. But that doesn’t mean you can release a shitty, buggy product with a generic ui and a poor ux. I think there is a fine line between releasing something that fundamentally works and provides value versus being too spartan, disjointed, that leaves the user disappointed and the company with a missed opportunity. Good design always matters.