That's incorrect. You can buy pre-approved modem setups, eg the esp32.

You are mistaken.

Yes, you can use pre-approved modules, but your new assembly still requires a spurious emission test (in place of a full emission test). It's a cheaper, faster, simpler test, but approval is still required to sell the new product legally.

Nope, he is right. If you use that chip you have to get it certified because the traces on the PCB can cause EM interference. Changing the housing of the product can also chance the EM interference so you have to get it recertified before you can sell it.

The FCC is a massive regulatory moat against hobbyist electronics. You have to make something expensive enough or with enough scale to make enough profit to be able to pay for the expensive testing. If you fail the test and aren't able to fix it on site all of that money will be a waste and that will have been a waste of money.

Also in order to use Bluetooth you will have to pay a few thousand dollars in SIG fees to properly license it without infringing their IP.

i personally think its a good thing that goods sold commercially are not going to start basking my other electronics in random rf.

Yes, but I don't believe to achieve that with a less restrictive and expensive system. Right now if you upgrade your graphics card in your computer you can not sell your computer to someone else without paying $$$$ to get it certified. I think some rules about what kind of derivatives works you can make from already certified electronics would be beneficial.