The thing with kana, is that it's a syllabary.
Because it can only tell you how it would sound like, it can't always convey how a word could be spelled as intended in romanji.
That's why we got the whole Aeris/Aerith debate, until Square finally settled with the latter, btw her name is written as エアリス.
Now for the whole Oruku/Ork/Orc thing... オルク/オーク
For that matter, we already established that オーク stands for the species from the beginning from context alone, so either Orc/Ork works just fine. Even though one could write that as [Oak], or [Auc]tion (オークシオン).
As for オルク, in Japan, Warhammer 40k/Fantasy tends to use this "spelling" for their Ork/Orcs, so it's perfectly fine to use that too.
In the end, spelling doesn't really matter as long as it is phonetically the same.
The issue here is, everyone already got used to/accepted the established spelling utilized by ieatloli.