OP here. IMO, I think the reason Venmo trumps is because it's P2P payments rather than for retail / enterprise. Most of the hacks using Venmo are about tipping your friends or discouraging bad behavior, etc.

Plus, Braintree / Venmo are frequent sponsors.

There should be some asterisk or something next to tech that is a frequent sponsor. That influence severely distorts the conclusions. If we're discussion auto racing and Hyundai was giving out free cars, then would that mean that Hyundai was the best race car because everyone was using it? The intent of this study isn't to see how effective contest sponsorship is, it's to get an idea of popular technologies. Sponsorship non-disclosure paints an inaccurate picture. i.e. Azure being so popular when in the real word, it isn't.

Absolutely this. Sponsorship information completely changes the picture.