Can one supplicate for the removal of illness from all Muslims, knowing that this illness afflicts only some of them, and is this supplication a form of disrespect towards Allah's power?

There is no objection to asking Allah for well-being and safety for all believers from a specific disease. This is not considered asking for the impossible, as no text has been received stating that some people must be afflicted with this disease. The basic principle is the permissibility of supplicating for the entire Ummah, as the Prophet, peace and blessings be upon him, used to supplicate for his Ummah in every prayer.