Every customer’s data systems and requirements are different. You can build a consulting company that way, but not a scalable product company.
Believe it or not, this comes from my own experience.
a scalable product company
If you're building a scalable product company your first customers are your best evangelists. They're the ones you need to cultivate and nurture to take your message to a wide audience. Wider than you can connect with without them on side. That's why you have to do things at the start like emailing and talking with them personally. You can't do that when you have 1,000 customers, but you need to do that when you have 3.
Did PG say to do that?
You are on YC and appear to be disagreeing with PG's "Do Things that Don't Scale" article: https://paulgraham.com/ds.html so people jump to conclusions even if you don't.