I don't think it's unreasonable to say that some autistic people have more disabling symptoms than others, or that someone who can never live independently is not affected differently than someone who can work and manage a family. The argument for the removal of the functioning labels and categories is simply that nobody could draw a line.
There was no consensus amongst psychologists and neurologists about where the difference actually lay between Asperger's syndrome and classic autism. Some people drew the line at whether or not a patient is verbal, others based on IQ, others based on the age of diagnosis. None of those are particularly reliable. When it comes to speech, a nonverbal child will not necessarily be nonverbal for life, and the old classifications don't account for autistic people who are semi-verbal. IQ only measures some facets of intelligence, and doesn't inherently correlate to one's ability to function in daily life. Age of diagnosis relies too heavily on doctors' opinions than the patient's symptoms. Numerous people suggested I was autistic from the age of four, but our family GP refused to refer me further because he "just knew" I couldn't be autistic. We know now that I almost certainly would have been diagnosed then, but instead I got by until my teens when everything fell apart. People's functioning levels can change over time as well. I have one family member who was diagnosed young with a more "classic" presentation, but with support and appropriate education she would no longer fit those classic criteria. I was diagnosed with Asperger's, and I have meltdowns, I am unable to keep a full-time job, can't drive, can't reliably provide food for myself, struggle to communicate even with my close family and two friends, need a chaperone/advocate for medical care and other appointments, and require daily support to function in life. Despite all of those needs, I was considered "high-functioning" because I'm good with words. That's not to say I consider myself "low-functioning" either; if we had to go back to those labels, I would like a "mid-functioning" category for those like me who fall between the two.
That said, I do think some differentiation needs to be made so that people with "classic" presentations and symptom profiles can receive adequate support and so we can ensure that neither the autistic community nor the medical community overlook such people. My favourite model is the "support needs" framework, in which differentiation is made not on the "severity" of symptoms but instead the level of support and treatment the patient requires. Those who need full-time care, adapted education and communication assistance would be considered "high support needs," people like myself and my family member who need part-time care and social/community assistance would be "medium support needs," and someone who functions relatively well with the assistance of anxiety medication and as-needed counselling would be "low support needs." This would allow support to be better targeted at those who need different things without taking such a prescriptive approach as previous diagnostic labels. That said, I'm always happy to hear others' thoughts and criticisms as it's important to adapt ideas to make sure people wouldn't be falling through the cracks!