To say tuna sushi is a wash for thf is a bit exaggerated.
CHR is a 40% mod for DE, compared to DEX being a 30%. I think this depends more on your race.
As a mithra, this would actually help my DE more than a dex/agi + one, as I am already high in those stats and very weak in CHR.
That said, the difference would be marginal, and increasing your base STR would probably help w/ higher DOT.
You need CHR+4 to increase your Curing Waltz by 1 HP. CHR+2 for Curing Waltz II, CHR+1.5 for III, CHR+1 for IV. Best case scenario, you're adding 5 HP to Curing Waltz IV by using Tuna Sushi. Very marginal if you ask me, and it's even LESS effective on lower tiered waltzes (which you'll be using more often on DNC). I wouldn't go out of my way to use tuna over squid/sole.
As for THF, you lose DEX+3 from Squid/sole, which isn't worth the gain of CHR+5 for a SA+WS. You also lose AGI+5 from squid, which is even worse of a loss from TA+WS. Never use Tuna Sushi for THF unless you're solo, and even then, it's a very marginal increase, and I'm temped to say the loss of DEX (Dancing Edge has DEX and CHR WS mods) makes the difference a wash anyway.
Now for BST it's a different story, but if you need accuracy soloing, there are other greater problems at hand...
Bsphilar, BST tends to go extremely high acc, moderate damage for soloing. Constant steady damage as opposed to spike damage and the hate that comes with that.