I think it is ten years ago Photoshop added internal Open Type Format support. Before that there was some plug-in that handled the otf files. All fonts I buy these days are otf, and sometimes there are no alternatives, I mean ttf-fonts are not made any more by some type foundries.
Photoshop got it. Clip Studio got it. Krita got it. SketchBook Pro got it. Affinity got it. Otf support. And most other graphic software.
Working with pictures and text integrated, like I do, means you have to use one single program to test things out and not switch back and fro from Painter and another program for texting. It take too much time. All the other software mentioned above are capable to handle otf fonts (and also have good text handling).
I must say, I do not use Painter a lot these days because of very bad text handling and no otf support.
Yes otf fonts, and using specific characters for artwork, would be beneficial to Painter users.