I don't think its a big deal that the PS5 first week is lower than the PS4 first week when you consider the amount of countries Sony is selling in. The PS5 will continue to expand the market which will make up for declining Japan sales.
Its not like Capcom or Square are abandoning the PS5.
I consider it a big deal. The way Sony handled this, it will be quickly established for all the small and midsized Japanese publishers that returning to PS exclusivity is absolutely not an option, rather they will double down on getting Switch versions out day and date with the PS versions. And in turn the global perception that Switch is the console to play Japanese games on will only grow.