Graces F had a very mild opening back then.
Zestiria is standing >550k outside Japan with 300k being from Steam.
It wouldn't surprise me if Berseria was to do half what Zestiria did on PC, now on PS4 a slight decline was to be expected at first but longterm sales should help it remain steady at least, if not it's rather worrying.
On the same timeframe (one year) 300k across PS4/PC would be a dissapointing result, anything below a disaster.
Overall the series wil probably stay on a 500k-1M level worldwide for a long time.
First month
The concern would obviously be whether the games after Berseria continue the decline. If every subsequent game drops they need to reposition.