I think they can very likely match the TDP-down (7.5W,800MHz) performance of a Intel CPU from 2015 in a passively cooled iPhone. Now can they match the TDP-up (25W,2.8GHz,actively cooled) performance of this chip? Probably not.
That's the thing with Intel CPUs. There are a huge number of ways to configure them. Even knowing the part number is not really enough to judge what the overall system performance will be.
You're right but it's not a drop-in replacement: obviously being passively cooled into such a small device does not make it useful for constantly sustained performance. I'm confident aptly designed hardware surrounding those chips could have the characteristics we're looking for, but there are multiple barriers to break, such as a software <-> hardware synergy that is lacking for laptops, desktops and servers on the ARM side of things, as well as the current platform being largely good enough, so there's really no incentive (yet). IOW it's too esoteric right now to be of value, although some have tried, such as Scaleway, but that's not A11, and we all know where non-Apple ARM performance stands currently.
I am also skeptical. I would love to be proven wrong and see ARM as a successful competitor to Intel's monopoly first and the x86 monoculture second. (I'm also excited by AMD's recent successes in the CPU sphere. The Threadripper 1950X is a phenomenal CPU — 16 real cores at 3.4GHz is nuts and like nothing Intel sells.)
