If one did need to worry about trusting public wi-fi, one would also need to worry about trusting one's cell service provider or home / business ISP. And you can use a VPN for an additional layer of security over all this, but then you need to trust the VPN.
But I think you're largely correct. If I'm on wi-fi that I trust less than my VPN provider of choice, I use the VPN. And then I move on and live my life.