The problem is, when you are going for growth, you can't focus on the needs of one. You have to be able to take a higher level view, and build a product that can do the most for all of your customers. Sometimes that means cutting features, or at the very least making changes. If you had a product which was tailored for one customer, that fact may very well be quite limiting to expand to many more customers. Even if you build something that could do just as much for that early customer, the fact that you had to make those changes may be enough to sour the relationship and end it.
Again it's hard to know what happened in this specific case without details, but I would wager it was something along those lines. It's a decision not to be made lightly, but one you're likely to face as you grow a B2B service.
If you have a client like that who is hindering to growth, then a dominating strategy would be to spin-off rather than ditch. You can afford to put 1 or 2 people on that work while you build from what's already been done.
"We can't get feature X,Y, and Z completed which we think will get us X,000 new customers because of Big Client."
"Well, then fire Big Client."
"OK."
<months pass while new features X, Y, Z are built, Big Client leaves but it's OK b/c X,000 new customers are coming!>
"Hooray! We just released X, Y, and Z"
<crickets>
"Oh no! It turns out the features weren't actually what customers wanted or needed!"
<Hosed>
"...I can't help but ask, what did you expect?..."
I can't help but ask what the VC was thinking???
Serious question. I know we don't know all of the details, but this seems, on the face of it, a very bad idea. I would assume there must have been much better methods of handling that client than to cut them loose. A new free tier to generate growth maybe??? Or a tier on the high end which would serve to satisfy that client???
I just don't understand why "paying customer" and "high growth" have to be mutually exclusive??? They are not mutually exclusive in any other industry I work with. Not in the restaurant industry... see Chipotle. Not in the shoe industry... at least women's shoes. Not even bike components... SRAM. Even in industries that are notoriously difficult... like porn... growth and paying customers can coexist.
I mean if "$OUR_BIG_VISION" has no room for customers who pay you gobs of money? I don't know what to think of that.