Worth noting that the description in that doc is of a more capable vessel than suggested by the requirements of the public version of the surface fleet analysis though. Self protection makes it clear it is capable of protecting escorted vessels , over the horizon strike on land targets is also spelled out. If the additional capabilities are delivered on time and without compromising undersea warfare that would be a big win for the RAN.
I would agree the upgraded Mogami is a more capable vessel than the original Independent Analysis into the Navy's Surface Combatant Fleet envisioned. That is a good outcome.
The over the horizon aspect to the strike capability aligns with the standard type 12 missile that Japan fields on the classic Mogami. It has a range in the 300km plus zone for both maritime and land targets, which is thoroughly over the horizon.
I personally think the jury is still out on the NSM option. Japan has previously stated a consideration of integrating the NSM into the base Mogami platform. I'm unsure if that was to entice Australia, or for a genuine strategy of building in future flexibility. Either way, if it becomes part of their base platform, then it should also be available to us.
If we don't fit NSM to the GPFs, it potentially makes our NSM factory somewhat of an orphan, with a very limited use. This could prove to be problematic for the broad integrated strategy.
In regards to escort duties, that was always part of its function, I've pasted the original scope for the GPF from the IANSCF below.
At least seven, and optimally 11, Tier 2 ships, optimised for undersea warfare, to
operate both independently and in conjunction with the Tier 1 ships to secure
maritime trade routes, northern approaches and escort military assets.
Given that Japan has not yet commissioned a Mogami with a working VLS, I'm not sure there is any guidance on what missiles it will be configured for (let me know if I have missed something on this). I think the first VLS has only just been installed on Niyodo, but no tests to demonstrate what it fires.
Japan uses the ESSM on all its other VLS capable ships (albeit via an Aegis combat system), so one would think they will continue that with the Mogamis. They also use the SM series, so it's not unreasonable to think it should also come with SM2 connectivity. There is a lot of American technology in the Mogami combat system, so one thinks this this should not be a difficult path. I assume they have been developing this integration for a while now.
The Australian government has been aluding to ESSM by stating a capacity for 128 missiles in multiple media releases. That can only be an ESSM package.
A Mogami, with an ESSM and SM2 fitout across a 32 cell VLS would provide very capable escort defence.
The other interesting point in the media release was some clarity on what the next stage of contract negotiations will involve. It was specific to the three offshore builds. That seems to shut the door on additional offshore hulls, however they may be included as contract options to be activated later (I think the Hobarts originally had a similar arrangement for the unfortunately not accepted fourth hull). It also gives guidance that contracting for the Henderson phase will be executed later and not part of an overall full program contract.
