Good question. There have been some knock down drag out arguments over this one in the past on this forum.
My advice. Decide if you want it to be a 'service disconnect', for any reason. If you do, bring the neutral there and put an MBJ. If you don't then run an EGC from the other service disconnect and leave neutral floating. Whichever you want, run it by your AHJ before installing. If it's a small system and/or you don't really have time for that, plan in such a way that you could do whichever the AHJ asks.
For what it's worth, in the 2020 NEC draft, the CMP seems to be moving away from the opinion that it's a service disconnect, without quite making that explicit. On the other hand, the definition of a service looks to be changing and that will take away one of the biggest arguments that it is not a service disconnect.