Just to add again the opposite approach:
I think it is bad sportmanship when one ruins a good game by perpetual raichi. Perhaps the best remedy IS to make it really perpetual: "if you don't give up a game which you have lost, I won't grant you a draw".

You just can't expect one side (black) to play perfect - and we do not even know if perfect play can prevent this kind of easy draws.
OF COURSE players with lower ratings play suboptimal (we all do of course, even ughaibu makes mistakes) but if the black player prevents the king to march out of the board and will eventually close him in and kill (if necessary) the remaining white soldiers, black played better and is the winner.
That the black player could have prevented perpetual raichi doesn't prove white deserves the draw.
Why should black not only have to prevent escape but also perpetual raichi? Isn't it difficult enough for black? Are there not enough drawing possibilies for white without the easy perpetual raichi?
With one soldier (like soldier d1 king d2, soldier d5 king d6) one can try to get a draw out of this: not only by a 4-soldier construction in the corner but also with more soldiers left then black can safely capture.

Look at my two games against WhisperzQ. In both games the white player could have perpetual raichi'd in an uncomfortable position. Are you seriously blaming the black player for that position to occur?

To sum up: having to prevent perpetual raichi puts an extra (too heavy) burden on black, since it is too easy to achieve.

It IS a real problem, for it is no longer just an incident; some players even go for perpetual raichi from the beginning. It influences the games too much: "I should play this good move, but can I trust my oponent not to perpetual attack?"
A solution would still be to make an extra Tablut variant with a rule against perpetual raichi or to implement this rule on the existing variant.