Yes it is. otherwise people wouldn't be buying it.
People who are willing to buy the IPhone bearing its cost in mind are not comparing it with the 830. i would at least expect them to compare it to the 930.
It is like saying is the Mercedes S class 3 times better than a BMW 5 series. well...those two products are not even competitors.
We have to compare the S class with a 7 series, that's when we start to make sense.
OP even wants feedback comparing the 640 XL with the IPhone 6....... :S
The only people who are comparing the iPhone 6 to the Lumia 830, here, right now. 99% of people who own an iPhone have never even heard of the Nokia Lumia 830 and if they had given it a chance I guarantee a large portion of them would be more satisfied with the Lumia 830.
The reason Apple has such a large fan base is marketing, and timing. They came in at the right time and spent billions on getting the iPhone out there and rested a fan base who would die for Apple. Samsung did the same thing, and although their fans aren't as sheep-like, they were more successful market-share-wise.
I've used both phones, and I firmly believe the Lumia 830 is the better phone. If the iPhone 6 was priced closer to the Lumia 830, it would be a harder battle. So of course they can be compared, because the Lumia 830 honestly can compete with the iPhone 6 in a lot of ways.
Design wise, it's a matter of opinion. I prefer the warmer, sturdier feeling of the Lumia 830, but I quite like the iPhone 6's curves. I don't like the little camera hump on the iPhone, though. I think the camera housing is way nicer on the Lumia 830.
Camera wise, I think the Lumia 830 edges out just a little. The iPhone 6 is faster giving it some points but I've compared both myself and the Lumia 830 is more detailed and deals with lighting way better. And, of course, the Lumia 830 has OIS, which a phone nearly twice as expensive does not, and never has (excluding the Plus). Features, the iPhone 6 is a little better, but the Lumia 830 has some awesome features like Rich Capture and Lumia Camera can only get better. Also, audio recording is better on the Lumia 830. Oh, and you can't forget the two-stage shutter button. That's INCREDIBLY useful.
Performance is the one area the iPhone wins hands down. Sorry, 830, but your Snapdragon 400 is found in phones Hal YOUR price. It's good enough, but not as good as it should've been. The iPhone's A8 is way ahead here.
Screen wise, the iPhone 6 is just a bit ahead. It has a higher resolution, and slightly better color calibration, but the Lumia 830 still has a great screen that can at least compare to the iPhone 6, and wins some bonus points for being able to fit a 5inch screen into a body nearly the same size as an iPhone 6 (those top and bottom bezels are just huge on iPhones).
Software...I think the Lumia 830 wins hands down. Yes this is my opinion, and I know that iPhones have better support and more features, but I can't stand the restrictive nature of iOS and I hate iTunes. So here, for me, the Lumia 830 wins.
Extra features...Lumia 830 again. It has NFC and Bluetooth, same as the iPhone, but also has microSD card support, wireless charging, and a removable battery. And why none of these are strictly necessary, someone will always find them useful and important.
In the end, the Lumia 830 wins. If the iPhone 6 was in a similar price range, it might be a tie or honestly the iPhone 6 would probably win. But they're not, the iPhone is twice the price. In that aspect, the Lumia 830 kicks its sodding teeth in.