Okay... something is off here. when I look at your phone settings page, it looks different than mine.
See the attached screen caps.
Our phone preferences are different.
Our wifi preferences look the same.
This thread looks the same.
What is that little blue wifi icon/notification in the bottom right of your screen?
And... what is a captive portal? Is that some type of VPN thing?
I don't have either of those things, ever and I have used wifi since day 1 as my data connection of choice. I used it witout a SIM, so there was no phone data, I used it with a T-mobile SIM and had Edge data, and now I am using it on Sprint and have 3G data yet in every case the wifi worked and connected exactly the same way.