elfprince . parted
may be a component or backend (do I have the language for that function right?) part of any given installer. which would mean both methods work. I have no idea where I got in the habit of bringing to the solus installer a perfectly formatted GPT disk...when it was going to do it itself anyway? Redundant then.
[that said I never made my own boot/root partitions, always let installer do what it wanted.]
You are probably right. If someone brought to the solus installer an entire FAT-formatted disk, and told the installer to put Solus on the whole disk, then I imagine Solus would do the GPT part. My own prep, if it's redundant and it probably is, is just habit for sure.