This question looks like a simple product-versus-marketing debate. In practice, the answer depends on what each term means.
Product quality can mean two different things
If product quality means pre-launch perfection, it can slow learning down. A startup can spend too much time polishing details before it knows whether the problem is real.
But if product quality means the minimum core experience that repeatedly solves a real customer problem, it becomes a condition for useful learning. Without that core experience, user behavior is hard to interpret.
Marketing can also mean two different things
Marketing can mean paid acquisition, large campaigns, and broad awareness. If the product cannot explain or deliver its core value yet, that kind of marketing may only create churn and confusion.
But marketing can also mean customer interviews, message tests, landing page experiments, and small-scale demand discovery. In that sense, marketing is not separate from product learning.
The stronger answer is conditional
An early startup should invest enough in product quality to make user signals interpretable. But it should not stop customer contact. Small-scale discovery and message testing should continue while the product is being shaped.
Do not scale acquisition before the product experience can explain the signal. But do not build in isolation either.