All the medical conditions a person claiming DLA has should always be included in the information on the claim. This is to give a full picture of how the need for care and the mobility problems may have arisen. Other conditions which cause mobility problems and over which there is no controversy as to the physical cause are particularly important. This section does acknowledge that groups such as your own have an important role in this area. No one should be put off from applying at all.
Bad experiences do, unfortunately, tend to be more quoted than the good ones.
You advise that evidence given should be based on worst days. It is, of course, essential that this information is given but evidence as to good days and an estimate of how many of each is necessary for an accurate picture. The comment is made that someone who is well enough to apply will not qualify. Since DLA is a benefit for severely disabled people a great many recipients are not well enough to apply personally. The comment clearly results from the frustration felt.