In Japan agriculture is heavily subsidized, in particular rice production. Stuff that is not heavily subsidized focuses on high margin premium. They can't compete on volume/price but can on quality. After eating expensive apples or grapes there nothing really compares anywhere else
Rice, unlike tea, is a defensive measure for times of crisis. Even as Japan imports food, the point is whether the country can quickly mobilize and ramp up to essential food crops. The point is having options and a hedge, which allows you leverage during economic negotiations for other things.
The percentage of imports you can have should be bounded by the runway and time horizon you have.
It seems Sri Lanka went all in on one crop without a hedge, and it would infeasibly take years to convert.
We have had enough bad experiences in the past however to give up having some level of self-sufficiency.
If you ever wondered why nearly every European country is in the EU, except Norway well there you got part of it he reason.
There are many others, to be fair: Iceland, Switzerland, most of the Balkans, parts of Eastern Europe, the UK, and at least 5 microstates.
Are you saying EU membership could affect Norway's agriculture?