As mentioned elsewhere, Japanese SaaS rarely ever deal with timezones because there's only 1 timezone. And I think this was originally built this way (using YYYY-MM-DD for filtering) to avoid having to think about time zones, with the assumption that the YMD values were all that mattered.
In our instance, it doesn't matter where the dashboard is used. It's a service built in Japan for people living in Japan. The dates are stored in Japan Standard Time in the database, so even when the dashboard is accessed from outside Japan, the user is only interested in filtering the values based on Japanese dates.
As mentioned elsewhere, Japanese SaaS rarely ever deal with timezones because there's only 1 timezone. And I think this was originally built this way (using YYYY-MM-DD for filtering) to avoid having to think about time zones, with the assumption that the YMD values were all that mattered.
In our instance, it doesn't matter where the dashboard is used. It's a service built in Japan for people living in Japan. The dates are stored in Japan Standard Time in the database, so even when the dashboard is accessed from outside Japan, the user is only interested in filtering the values based on Japanese dates.
Otherwise, I agree with you.