I think this may be something I miss when my SE finally shows up. Android allows the use of a myriad of launchers so you don't actually need to go near touchwiz. Not sure what you mean by locked down though, bootloader and recovery are the first things I unlock on any android phone. Again not sure what I'll do with the SE although one minor reason for choosing it is to remove the ability for me to spend hours putting custom ROMs onto it.
unfortunately, Touchwiz is far more than just a launcher. It's embedded in the OS at the core, so you can't get away from it by installing Nova launcher, Google Now Launcher, etc. Touchwiz is getting much better but still causes performance issues and degrades the functionality of the device over time. My last real world experience was owning the Galaxy S6 for ~4 months. I did really like that phone and 80% of the time, it was one of the smoothest Android phones I've owned. But about once a day (sometimes twice a day), the phone would just start lagging like crazy to the point where it would take 5+ seconds for anything to respond to a touch or action. A reboot would clear it up, but this happened quite often. And not to mention the RAM management issues that were seen on that phone.
with regards to his locked down comment, current Samsung offerings (at least some versions in the USA I think) don't allow bootloader unlock or sometimes even root access. For an android modding enthusiast, this is a non-starter.
with regards to OP. I have owned a lot of android phones and several iPhones since getting the iPhone 3G in 2008. For me, iMessage, iCloud Photo Sharing, and FaceTime are the reasons I stay on iOS the majority of the time. ~95% of the people (family and friends) I communicate with often own an iOS device. We share lots of multimedia (videos and pictures) of kids, vacations, etc. as well as FaceTime regularly. And I do like the hardware of my 6s and really like iOS 9 as a whole... the design, functionality, etc. I do like Android for the customization. I always install nova launcher first thing and really enjoy using the myriad of icon packs that are in the Play Store.