How to tell if our SaaS for designers has PMF or a marketing problem

[NathanM]

I'm a co-founder of an early-stage SaaS startup targeting freelance graphic designers, and while we have a small group of passionate early users, our growth has plateaued. We're struggling to determine if this is a marketing problem or a fundamental issue with our product-market fit. For founders who have navigated this ambiguous phase, what specific metrics and user feedback channels did you use to rigorously assess fit? How do you differentiate between users who love a niche feature and those who see your product as a must-have core solution, and what experiments did you run to test new value propositions or pivot your target audience without alienating your initial supporters?