A question.
It appears to me that the most popular interpretation of SMT, or HT in this case, is that there is a main thread and the 2nd one gets the unused resources. In other words the additional thread on the virtual core has less resources to operate.
No. The back end of the CPU doesn't even see that there are different threads. Both threads have equal priority. The result is often like that statement, but that's not what the CPU is doing.
I have always believed that there is no main thread but [2] threads vying equally for core resources. If HT gives, say a 30% increase, then, by my understanding, assuming equal loads, each thread will run at 65% full single thread performance. Am I correct?
It can be like that, but usually it's not. Usually, the performance hit is fairly small, and both the OS and many multithreaded programs don't try to overload the CPU. So, you may see that with video encoding, but are unlikely to see that with gaming. The +30% is a typical expectation. Usually, it's a bit less, sometimes it's more. Usually, the benefit of it is that processes that can come in and take up a lot of CPU time, but don't use much of the CPU's execution resources, can run alongside processes that do use a decent amount of the CPU's resources, with very little performance impact. Try to search for reviews comparing CPUs with background applications running, to find examples.
For one example, memory management, such as allocating and freeing, defragmenting (AKA compacting), and garbage collection, use a lot of total CPU time, but have absurdly low IPC, just by their nature, and tend to not be too bad in terms of cache usage. With SMT, that code can do its thing, and hardly affect anything else running. Another would be antivirus, which often wakes up several threads, or in MS' case, spawns a bunch of separate processes, each making a lot of calls to the OS, that end up using up a bunch of CPU time, to end up doing very little. In many of these cases, you don't actually have multiple programs you are, or even can, test performance against, to say that each thread is X% as fast (in most cases, the larger concern is whether they remain "fast enough" that you don't notice a slowdown under moderate loads). But, it is possible to benchmark multithreaded programs in realistic environments, or repeatable amalgams of them, and show more consistent results with SMT than without.
Now, as far as getting rid of HT, if they can add more actual cores, instead, economically (the power use alone may be an issue that favors spread out non-SMT cores, once 8C and up becomes mainstream), that'd be perfectly fine, even if they left SMT only in workstation and server chips. However much I may roll my eyes at Intel's market segmentation efforts (niche sharing among SKUs will not be tolerated!), SMT vs. non-SMT is a perfectly good way to split product lines, and more actual cores is always better for performance.