I couldn't agree more. It lacks any form of internal expansion (People talk about Thunderbolt as if it's a magic fix. It's a bandwidth-limited compromise and that's like Batman talking about money as if it was a superpower).
The CPU-only performance is rapidly becoming slower than the higher end i7-based offerings in the Macbook Pro and iMac range unless you go high end, then used 2012 Mac Pros that DO offer vast internal expansion are available still in the used market that spank all but the 12 core model.
It's rediculously over-priced no matter what manipulative figures someone cooks up by adding displays etc... to artifically inflate the cost. I was expecting it to be cheaper than it was by a huge margin due to the lack of internal expansion and the cost/compromise of Thunderbolt only solutions to make up for it.
As it is, it's a video-orientated workstation that's of little use to a lot of people the previous Mac Pro was perfect for unless they have money to burn.
Ever hear the phrase, "Can't see the forest for the trees?". That applies to your statement.
As the post above states, all internal and external expansion is bandwidth-limited. 20Gbps is actually overkill for most PCIe peripherals aside from GPUs. Nearly any PCIe device that you'd buy to put into a TB2 chassis would work just as well. Video capture cards, Audio interfaces, Pro Tools HDX cards. As long as it works on OS X, you're good.
And I think you're exaggerating quite a bit on the CPU performance. One benchmark number does not tell the entire story. Just as much, you and many others here fail to realize that there is such a thing as a "thermal constraint" when dealing with computers. The MBP and iMac CPUs are extremely thermally constrained because of their enclosures. You simply cannot use large amounts of processing power for long periods of time on these systems without the chips scaling back so they don't overheat. So, while you can look at one benchmark and say, "Hey, this Haswell Core i7 in my MBP is slightly faster than a 4c nMP! What a waste of money for that machine. Hardy har har, who would spend more money for a slower chip?", the guy who has a nMP and does 8-10 hours straight of processor intensive work is still humming along nicely, while your system would A. Be a hot, loud mess at that point and B. Be scaling back your CPU capabilities so you don't melt its lifespan out. If you cannot take advantage of a system that won't scale you down due to heat, then simply, the Mac Pro is not for you.
And it's not overpriced either. Sorry, but that's an opinion based on wrong facts.