Are the newer Galaxy's comparable devices to the latest iPhones? I'd say they are the Android equivalent---and by that I mean they are the best hardware available running Android. I'm an iPhone user and big fan of both the iPhone hardware and iOS but even I can acknowledge the hardware itself is better on the Galaxy (battery size, display, camera, display size/overall size, waterproof, plus it offers expandable memory).
All that being said, I don't think the latest Galaxies are a 'threat' to the iPhone, because in the vast majority of cases, it comes down to OS preference. Samsung has arguably offered better hardware specs for a few years now and that hasn't significantly moved the needle. If last year's camera wasn't enough to make you switch, this year's model isn't offering any revolutionary changes that'll make you switch either. Same goes for the display, etc. I think OS preference is a bigger factor than hardware specs. If people are going to move away from the iPhone or iOS, it's going to take some revolutionary element in ANDROID that people feel they must have and can't live without. That isn't there presently, IMO.
And to be clear, I'd apply this same argument in the other direction. There is nothing 'revolutionary' in iOS 9 (and doubtful in iOS 10) that will likely sway Android fans to move to the iPhone.
The biggest threat to the iPhone (and ironically to the Galaxy/Note lines) are not each other but rather influx of much higher quality 'mid-range/mid-priced' smartphones. When it comes down to it, in most cases the greatest factor in the buying decision is price and now that consumers have a very good smartphone experience available at a significantly lower price, I think you'll see the largest growth in this segment of the market, at the expense of traditional high priced flagships.