Kurotowa
Legend
As I did mention in the fourth paragraph, Artillerists can't use it well because their Arcane Firearm is specifically restricted to Artificer spells, and True Strike isn't on the list. AFAIK picking it up from a race or feat doesn't make it an Artificer spell.You're missing a couple of options. Celestial warlocks can use it in place of Eldritch Blast at up to level 10, and Artillerist artificers can use it with their staff firearms (and IMO should be allowed to use crossbows or muskets as firearms) - and non-battlesmiths might want to use it with actual firearms. Also dance bards can go True Strike as a legit option and have a mixed weapon and unarmed style.
You're right that there's a narrow synergy between Celestial Warlock and True Strike, but I don't give it much weight. It gives up all the Eldritch Blast add-on invocations, and if you want a melee playstyle with a Warlock just take Blade Pact and do it better. With Pacts being invocations now there's little upside to not taking Blade Pact.
Dance Bards have the same MAD problem as Eldritch Knights and Bladesingers where you're forced to mix attack types. It's viable, but not particularly strong. But on reflection I may have undersold it. Still, it's pulling in two directions at once, and I never like that.