You are jumping way ahead in the workflow here, where thunderbolt is valuable is in the before editing stage. Say you are on location you have a laptop with external hard drives, you are getting lots of photo raw files and or video files. As you fill up memory cards you are transferring those cards to your external drives via your laptop. You may want this done quickly.
Then later when finished in the field you come back and transfer all that data onto your home base office long term storage setup.
I have no idea what the original poster is doing, but thunderbolt is useful on location.
In my case personally I can compromise on transfer speed when at home so I can accept the lack of thunderbolt in my Mac Pro, I wouldn't buy a laptop these days without it though.
I totally agree that we should not compare internal vs external. They are for different tasks.
However, in your example. The initial transfer speed should be limited by the memory card. I don't think there is a memory card that can saturate a USB 3.0 connection.
The 2nd transfer may able to utilise the Thunderbolt speed if the external drive is builded from a high speed PCIe SSD, which is a bit rare if the aim is to relief the memory card's space. And as you said, the extreme seed isn't that important at home. In fact, I did google a bit about protable Thunderbolt storage. And surprise that a 2017 review rated a 3xxMB/s speed as very fast (full score indeed).
I am not saying Thunderbolt speed is completely useless in real world. However, it seems not that useful for protable storage at this moment. And when the main stream storage able to saturate a USB 3.0 connection. We may already able to install a USB 4.0 card in a PCIe slot.
And if TB is going to the USB-C form factor, and all we need is just the ability of connecting a storage (but not eGPU etc). We can always install a USB-C card into a PCIe slot.
PCIe slots may be an old technology, but it's still the best component to keep a computer up to date so far. With the PCIe slot, there is virtually zero need to have Thunderbolt (or course, if something like your company only provide you Thunderbolt equipment, then that's a must for your workflow).