Problem is the battery and storage degradation is very real. While a simple factory reset solves some of the storage fragmentation, you'll never get the original owner's same experience with the device (unless you won the used device lottery and received a barely used handset).
But something like an iPhone 6 definitely is a competitor against a brand new $200 Android device (and may receive security updates for longer).
Out of curiosity, when have you last used a 200$ Android phone?
The options available nowadays are pretty good with updates (from Android One initiative) and hardware similar to (in a few cases, significantly better than) last gen flagships.
I just bought a few for testing at work. There's the HTC EVO 10 for $185[1], the Huawei Honor 6X for $200[2], and the Motoroloa Moto E4 Plus for $130(!)[3]. I also got a Samsung S6 to test, but at $250 for a much older phone, I wouldn't recommend it (but it is a fine phone, it's what I've been using personally for a few years).
I just set them up today, but I have to say, the $130 price point of the Moto E4 is pretty enticing given it seems responsive and has a fairly large screen (and if you are fine with Verizon, you can get it for $70 no contract[4]). The H6 seems like the one aimed the most to be a flagship phone. Fairly polished, and with a rear fingerprint sensor (all or almost all the rest have a fingerprint sensor, it's just on the front).
Edit: Whoops, the Verizon link and price is for the Moto E4, while what I purchased was a Moto E4 Plus, which Verizon has for $110[5]).
This makes some sense. A few months back Apple was found to be limiting the performance of iPhones with degraded batteries. A fresh battery wouldn't have that issue.
