What I can gather from online after making double sure is that the fonts PSP uses, even if in unique format, are bitmap, and not vector like most fonts used on PC's for past few decades. This means they are fixed size 2D assets much like the HUD and anything else with the game and most you can wish to do is find a high res texture modpack that includes the font, use good upscaling or just get used to it. Emulating old systems, especially portables, will have this issue and if you want to fix it for every game, you get to playing no games from NES to even PS2.