Using image formats for texture formats is amateur game development. PNG’s are fine for icons or UI or while you’re still trying to figure out what you’re doing. Once you know, you switch to a faster, no translation required, texture formats that load faster, support physical layers, compression, and are already in BGRA format.
> Blender exports KTX2, your engine supports KTX2, Gimp exports DDS/KTX2, Substance Painter exports DDS/KTX2, three.js has a KTX2 converter.
If you're manually doing this conversion from source images to shipping formats your wasting your artist's time, AND, you'll likely lose the source images since people will generally only give you what's needed to build. "Hey, could you tweak building-wall-12.ktx?" "No, It was made in Photoshop and I can't find the file with the 60 layers so no, I can't tweak. Sorry"
And my out-of-the-box Gimp 3.0.4. doesn't have KTX export at all. Didn't check the other tools you mention.