It depends what you mean by "single thread performance". AMD's slides have the Ryzen 7 3800x beating the 9900K in single-thread Cinebench despite the boost frequency deficit:
https://images.anandtech.com/doci/14407/COMPUTEX_KEYNOTE_DRAFT_FOR_PREBRIEF.26.05.19-page-024.jpg
Cinebench is a consistent and repeatable benchmark. Anyone can download and run it for free. If AMD are somehow fudging those numbers they'll get exposed pretty quickly. I'd be surprised if they're doing that.
Cinebench is also, of course, one of AMD's strongest benchmarks relative to the competition which is why they use it all the time. So we can expect that other lightly threaded workloads won't look nearly as rosy for AMD. Still, with IPC and clockspeed improvements I don't expect there will be much in it with the exception of workloads that are impacted by latency issues inherent to the multi-die design.
RE 65W to 105W Ryzen for the Ryzen 7s, I noticed that too. The interesting thing here is that the 12 Core Ryzen 9 keeps the 105W TDP despite 4 extra cores and double the cache, all while dropping only 100mhz on the base clock compared to the 3800X. I wonder if AMD are trying to avoid too many different TDP brackets? I know they have 95W Ryzen 5s, but perhaps for the Ryzen 7 & 9 classes they want to stick to 65W, 105W and a future 125-135W rating for the 16 core premium parts. Just a thought. In any case, TDP doesn't necessarily relate to power draw, so I'd be very surprised if the R7 3800X and R9 3900X draw the same power under peak load.