It seems like they recommend splitting out the database at the start because using a managed service is much easier than properly managing your own production database.
Now a WD Blue NVMe does 95k/84k r/w iops at $215 and that's just off their website (https://shop.westerndigital.com/products/internal-drives/wd-..., may be more depending on shipping method...)
That said, it's not a fair comparison and I wouldn't want to run a big service on a single sqlite/nvme setup for more reasons than are worth mentioning, but not prematurely optimizing can take you really far - scale and money - with good design.