One example, the paint bucket tool does not anti-alias correctly in certain circumstancess so no matter the tolerance setting, you get either white outlines around your fill, or the fill explodes outside the lines and gets everywhere.
This is something solved by other software in the nineties but Gimp still hasn’t bothered to fix.
Is this a niche problem? Yes. But when trying to do professional work, lots of detail issues like this can add up.