how do you determine the right messaging in a highly competitive market where everyone has feature parity?
First, messaging shouldn't be so focused on features. It should be about the unique value you provide to your customers.
While features ARE part of that value, they're not the ONLY thing that adds value. This is particularly true in a saturated market with feature parity.
A few additional differentiators that you might consider:
Integrations with other owned products and/or lots of integrations with industry-leading products that your prospects likely have in their tech stack already
Ease of onboarding/roll-out/setup, particularly if you're in a space that's known to be more complex
Benefits like ROI, time savings, accuracy, etc.