I agree in general with much of what is being said here, but do believe there has to be some very good reasons for not achieving not only the solo standard, but subsequent exercise standards, in a reasonable time. Failure to do so may lead to consequences later, especially if the pilot is in an unmonitored environment.
The topic of this thread has been discussed previously and I included a story which may be worth repeating. Flyer43 may recognise the sorry tale.
A sponsored pilot at the school F43 refers began to fail to meet the required standard mid way through his course (CPL(H)) and after review and further training was chopped. Undeterred he presented himself at another school and after spending his own money and using rather more time than the minimum, reached the standard required for licence issue (obviously debatable.)
He then received a job offer with one of the major offshore operators (obviously not the one who originally sponsored him) and started his AS332 conversion. He failed to make adequate progress and his employment was terminated.
Fortunately for him (less fortunate though, as it transpires) he was taken on by a small air taxi operator in the SE of England and flew Jetrangers for a while. His final task was to take a group of office workers to a Christmas staff lunch at Leeds Castle. Shortly after take off he entered IMC and the problem was compounded by misted up windows from the wet passengers. Tragically he and his passengers were all killed in the subsequent crash into nearby woods.
This is a rather sombering and some may argue excessively dramatic story. However it does illustrate that not every one does have the apptitude to successfully operate as a pilot, and that those who are tasked to train, mentor and assess pilots have a duty of care not only to the pilots themselves, but to the pilots' passengers. The notion that someone can become qualified after simply throwing money at the problem is a dangerously misleading one.
However, I do agree that there are some circumstances, generally exacerbated by weather, continuity and instructor related issues where progress may be slower than hoped for, and the student should be encouraged that this is perfectly normal. I agree it's not a race, but lets stay realistic too.