Just my opinion, I have another take on Hickman's definition of Omega mutants that it means 'their current abilities to control their powers at certain categories' has reached a level of 'no upper limits'. However, any other mutant that is able to evolve and has increased control of their power may also reach 'no upper limits'. (It is not always about how powerful but unlimited potential and possibilities)
So, even Hope is superior than Rogue currently, there are still things that Rogue can do better and if she gains better control and power of them. She maybe able to reach Omega level some day.(You may think about if she absorbed Hope...)
And from a writer perspective if I list some Omega mutants that can't be surpassed ever after. This isn't good for story development for the future.
So, I would just take the list as 'the current' topmost mutants that can 'control their abilities' to a level of 'no upper limits' in this era.