Great question. I'd say the core of this problem is that Marketing has to play a role over the short, medium, and long term. And often time, brand marketing efforts require persistent campaigns over a longer period of time, so the key is to establish a baseline and come up with a few metrics to showcase along the way. Your end goal is to show that rising tide (your brand perception) is lifting all boats (including the revenue engine that is your GTM team).
That baseline is often best established with a Brand Perception study. You can do a lightweight one yourself on your site, especially if you're a self-service product with plenty of eyeballs, but my preference is to use a 3rd party agency to do the research, define the target customers, and then anonymously collect how your company is perceived across product, service, values, and even confidence in your ability to deliver value. Intermediate metrics like Share Of Voice and NPS are common go-tos to capture that overall "how is the world feeling about our company".
Another thing that helps me explain this internally is to apply a simple framework around marketing's value in SaaS businesses (especially earlier stage businesses):
- Support revenue formation: Tie your above brand metrics back to examples of how opportunities were won due to the awareness you drove
- Create brand awareness: Takes time and concerted effort to build an emotional connection with your company and create the "surround sound"
- Maximize engagement: Demonstrate that customers that hear about your consistently, understand your value/vision are more likely to spend and less likely to churn