All valid points Hiten Shah. Excellent analysis where I could see your Kissmetrics-oriented thinking standing out.
But it is a failure only if Joel and his team think so. Yes they could have got more but what if they did not want more? With a 50X, maybe they made tons of money that they would not know how to spend.
WhatsApp did not have a monetization model. All they had was a 1 USD per year fee. I know it is not a B2B product but is used for business comms anyways and is as horizontal as any communications product can be. Yet it got to 19B.
But again, excellent analysis that any growing SaaS company should be doing and of course, should be using Kissmetrics to do it as well. :-)