IMO it mostly depends how your son is feeling. If he's happy, there's no harm in treating the first year at school as a year for socialisation. If he's frustrated, disappointed with school, bored, then you need to get in there and do something about it, as much so that he knows it's not supposed to be like that as for anything you accomplish. This:
They are not allowed to read anything above a GRL I in kindergarten
would be an absolute deal-breaker for me: if I couldn't get that changed, I'd move my child.

I wrote here about my experiences with DS's (fantastic, I have to say) school at the time, e.g. here, here and here.

Good luck, and welcome!

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