Disappointed? How so? With the A10 Fusion Processor compared to the A9, I certainly noticed the performance when I upgraded from a 6S plus to the 7+. I don't think it was dramatic, but there is no question that iPhone 7 Plus is faster than the iPhone 6s Plus. When I upgraded from the 6S plus from the 7+, I wasn't expecting dramatic results, but I was certainly satisfied with the performance and and there is no other phone that is as fast as the iPhone 'A series chips. '
6+ --> 7+ is like moving from a minivan to a Ferrari in terms of performance increase. Clearly, you're not a power user or you would see a night and day difference unless there's something faulty with your hardware.
If you don't boot up large games or files, you won't notice much of a difference. But rest assured knowing the processor is ~138% faster than your previous phone, as well as more power efficient.
iOS10 runs pretty smoothly on my 6+ but even my gfs 6S is considerably quicker. My friend has a 7+ and its a country mile quicker. There is no way you can genuinely think the two are similar in speed.