The business plan for a startup pitching to a VC will look different than the plan an SMB submits to a bank
I do think the plan you linked to is more thorough than what the majority of SMBs will be writing. YC is another league of finance. Most SMBs I know are not very sophisticated
It also included a background check on the management IIRC
Can you link to an example SMB business plan? I once tried to help a neighborhood grocer with financing and I can assure you they weren't writing a sophisticated business plan.
No it's not. The point is that what most start-ups submit as a "business plan" is just a load of b.s.
The questions that are asked in the YC interview draw out the information that _should_ be in a business plan.