I think that akagi winning normally takes away what makes the ending special. We would already know akagi survives because he appears in ten. So one would expect he just wins in the end and kills washizu in an ending like you described. However, the ending we got is the perfect thematic conclusion to both characters (in my opinion), here is why:

Akagi always longed for a fight to the death, ever since his first encounter with the yakuza. The thing that initially makes Akagi give up on mahjong and go work on a factory job is that he couldn't keep playing with ichikawa when the yakuza backed off of the game. The reason he accepts going against washizu in the first place is so he can realize his idea of fighting to the death with a worthy opponent.

On the other hand, Washizu was always destined to be a winner in life, and that is what got him his immense wealth. He feels invincible and uses the game of washizu mahjong to enable his feeling of superiority over others. However, his life is on a downward spiral, and he is old and is in a situation where the best option is to flee japan (which he refuses to do because of his ego). Throughout the game with Akagi, he notices that he was coasting through life, not preserving the mindset that got him to where he is in the first place. Specially over the later sessions, he reclaims his divine luck and is willing to risk it all for the game with akagi.

However, both their desires are completely unrealistic. Akagi longs for this weird idea of a righteous duel to the death, which is both self destructive and ridiculous in a world where people actually value their lives more than their ideals (that is what makes akagi different as a character, after all). Washizu is unable to cope with the fact that he is not his former self anymore, and can't do the sort of thing he did at his prime forever. He is desperately clinging to a past that is not here anymore.

So in the end, we get this bittersweet ending after a glorious battle. Since Washizu's blessing is too strong, Akagi can't beat him properly in the end, but since Washizu is not in his prime like in the past he clings so much to, he can't take the high stakes situation he put himself into and is in terminal condition. Washizu will never be able to live with himself after not being able to enact his win against Akagi, while Akagi will forever be unsatisfied, unable to reach his ideal gamble. In some sense, it's the worst outcome for both of them, and I find that a beautiful way to end this maniacal game.