I don’t think it’s reasonable to expect disabled people to prioritise their work colleagues in the event that they have to go off sick for some reason - given that their disability will likely result in more sick leave than average
Nor do I, any more than anyone should. But there comes a time when anyone - disabled (which my colleague was not) or otherwise should have the decency to realise that if they are stressed by the day to day tasks that their job entails to the point that they are off work as often as they are there, then (a) they are not fulfilling their obligations to their employer and (b) that they are placing an unfair burden on their colleagues, and find another role. Not a lesser role, and not an unskilled role, or any of the other words you put in my mouth, but a different role that does not stress them.
Different tasks stress different people. You don't like it when I give examples, and I can't spell out what I am getting at in the case of my colleague so my hands are tied, but I'll try one more time:
Many people find public speaking stressful - I think it is one of the top phobias. If someone takes a job as a tour guide, or a barrister, both of which involve public speaking as a matter of routine, but goes off sick every time they have to do it, do you think that their colleagues should have to do their job for them, or do you think that they should find a different job? It would be good if you could answer this yes or no.
If yes, why do you think someone should get a barrister's salary when they are not going to court?
Would they not be better suited to working as a legal secretary? You might see this role as 'lesser' than that of a barrister, but if it is better suited to someone who is not able to speak in public, as their own role requires, what is your rationale for not suggesting that their legal expertise would not be better used doing that instead?