Have you had the battery checked to see if it's at EOL? If it's not, then the issues you're experiencing aren't likely to be related to the battery or the throttling feature at all. You'd be better off focusing on the standard troubleshooting steps.
I'm def being throttled. I start my phone as new with every new iOS, so I just started new with iOS 11 not to long ago. According to geekbench I'm getting a 1060 (should be 1471) single core, and a 1776 multicore score (should be 2472).
Also, on the geekbench battery benchmark (partial discharge test) I went from 100% to 20% in 2 and a half hours. I'm sure my battery is shot and has been for a while. I've been using a charging case for over a year.
I did take my phone to Apple (prior to the $29 replacement program) and I was turned away because my frame is bent (iPhone 6 bendgate issue) and they wouldn't be able to get it back together, which I'm unsure if that's true. They told me they can't change the battery and I'd need a total replacement for $325. I said no thanks, for that much I would just buy a new phone. I have a launch 6 Plus, and I now regret not making a big deal about the bend while it was still under warranty, I didn't think it was a big deal at the time.
I think I'd still going to change this battery myself after I get a new phone, but I'm not going to now just in case it really doesn't go back together.