I was referring to the controversy around those labels, which goes beyond just the scientific discussions. I wasn't thinking about anyone in this thread or on this forum (that I can remember anyway). Sorry for being unclear.
No I don't think we can easily measure severity of illness, although I'm sure it can be operationalized. What I mean is that since we know that the prognosis is worse, we can probably assume that the illness is also more severe. It's not a direct causal relationship at all, but my common sense says prognosis and severity are very much correlated.