So I found the actual website (in Japanese) that a travel agent would use to create a ERFS
https://entry.hco.mhlw.go.jp/

Within this, there is a FAQs for how to fill it in, and it links to here:
https://www.hco.mhlw.go.jp/faq/newentry.php

In the FAQs, the only thing about fhe tour itinerary (or flight and accommodation booking) is Question 3-8:

ERFSの申請時点で、ツアーの行程全てを報告する必要がありますか。
Do I have to report the entire tour itinerary at the time of the ERFS application?

ありません。ただし、ERFS上で、ツアーの行程の最初に滞在する滞在先及び滞在先住所を記載することを求 めています。
No. However, on the ERFS, we require that you list the place of stay and the address of the place where you will be staying at the beginning of the tour itinerary.

So the ERFS only asks the agent for the first night accommodation location, thats it. (if an embassy asks for more to get the visa, its up to them)

Now, that said, the sponsoring agent is wholly responsible for the Covid-related health issues of the tourist for the entire trip, including medical treatment, quarantine arrangement (it can only be in special locations), transport to quarantine (not via public transport), and any potential denial of service due to suspected Covid illness (they still do temperature checks at lots of places to enter, including hotels, which is why hotels would want to know who is the sponsor but this isn't possible if someone self-books things)..

So it would be pretty foolish for a tour agent to let someone float around the country without knowing their whereabouts, especially since the agent is financially on the line to cover the Covid-related costs in case the customer does not pay. And there is nothing on the ERFS (or for the visa) which asks about insurance, so again, its the duty of the sponsor to check and cover this (and it would be particularly foolish to not be certain that the client is properly insured).

Aside from being lax on knowing your itinerary, has JGA asked anyone yet about insurance?