When your prospects review your proposal, will they choose the service provider who is the most competent or the cheapest? To write the proposal that gets the job, you need to know what they value most.
There are two kinds of freelancers in the world. Those who work with a specific clientele, and those who serve a wider audience. The niche folks are pro niche and the generalists are pro generalist. But is there a wrong option? Which are you, niche or generalist?