For example booting linux and running a simple application can take many billions of cycles. You simply can't simulate that many you need something faster (You can simulate a few billion overnight with an appropriate server farm, but that's across many tests using many simulator instances).
I think there's a lot of interest in designing "highly regular" chips. And it's definitely possible to go quite far with open source tools. I've seen a 16-core general purpose chip with full 64-bit IEEE FP, ALU, and memory instructions operating at 1 MHz (real speed) as a gate-level simulation on a desktop computer. This could potentially be "running linux" at a reasonable (if sluggish) speed.
What's your point? The ASIC emulation market exists, there are several companies that build and sell ASIC emulators, and Xilinx and Altera cater to that market with dedicated FPGA devices. I'm not sure why you're arguing here.
You don't need emulation for simple stuff like Bitcoin miners or other small and/or highly regular chips. You use it if you develop a large SoC taking tens of millions of dollars to develop. It takes months after finishing your HDL code and before you get the first silicon from the fab, and you don't want to wait that long before you can start testing your custom software.
So, no, #2 isn't questionable, it's routine practice. In fact, the largest FPGAs by Xilinx and Altera are structured explicitly with that use case in mind.