I have the opposite experience wrt. ISOs and plain (dd) images. If I burn an ISO to a USB stick, I can use the whole stick. But if I burn a dd image to the stick, the size must match exactly, otherwise I have to futz around with fdisk and resize2fs. Sometimes a 4GB stick has less memory than another 4GB stick, so you can't restore.

And when creating images, you have to take extra care to zero out unused space, otherwise your dd image will not be compressible.

Frankly I just want a small file that I can right-click or drag into Rufus and burn my USB stick or SD card ASAP. I used to know exactly what was going on when making a bootable floppy; the file containing the bootloader had to be in certain sectors, so you had to create it with FORMAT, but all other files could just be copied on. I don't know if any special sector layout is neccessary nowadays, I think for EFI boot it just requires the EFI directory. And tools like Rufus probably just copy file by file to the USB drive, not sector wise.