That is a myth that has long been debunked. There are even videos of it withstanding 200 degree temperature changes over just a few seconds time with zero issues. A few people either had defective phones, or unknowingly cracked their rear-glass visor - no big deal. I've already had my 6P in and out of 50-60 degree rapid temperature changes multiple times with zero issues. Seriously, don't worry about it. You bought an iPhone 6S even with the serious overheating & battery drain issues, the 6P doesn't have anything like that
I had my 6P next to a 6S Plus and the 6P did everything noticeably faster except load a couple games and cold-boot from a powered down state. Opening regular apps, switching between apps, loading content heavy apps & web pages, web browsing, etc. was all appreciably faster on the 6P. Fingerprint reader speed is about the same (instant). Camera is objectively better on the 6P. 6P has a *way* better screen, not to mention bigger, with the same device footprint as the 6S+. Speakers on the 6P are a lot better.
Mostly it comes down to your preference between Android and iOS, because both are premium phones. Having full control over your phone rather than what Apple tells you is best for you is a huge draw to Android. Beyond that, if you are concerned with hardware features (screen, speakers, camera, etc.) the 6P comes out on top pretty well everywhere but neither is going to disappoint.