The criticism of Kate's work history had nothing to do with her being a commoner. She was applauded for being a commoner by many, the whole Cinderella story quite popular now for people watching royal weddings.
If Kate had been as young as Diana when she got engaged, maybe no one would have blinked. But a 28 year old who spent less then a year as an accessories buyer and then is said to have worked 'for mom and dad' in an undisclosed position? When you go into an interview, any blanks on your resume are red flags. Kate's had gaping holes. If she had been actively involved in charity (other then attending then charity ball) or still studying, people would have looked over it easier then not.
Even among the aristocratic royal brides of this generation, most of them have a descent resume. Countess Mathilde (future Queen Mathilde) was a speech therapist for a number of years. Countess Stephanie de Lannoy worked with an investment company in Brussels after completing her masters degree. Heck even Diana had worked in a nursery school and as a cleaner for all her young age when she got engaged.
For most people the time when women went to college 'to find a husband' and then waited for a ring died a few decades ago. Even among the previous generation most of the royal brides worked before marriage.
Unfortunately the image was painted of Kate as 'waiting for the ring', living in a flat paid for by her parents, and available to William.
While most people are all for the modern royals, marrying commoners for love and not titles and so on. With that goes the thought, or at least hope the women are modern as well. Women with careers or life themselves, a work ethic and drive they bring with them to the job.
The current batch of heir's spouses, and new queens include:
-Maxima-masters in economics, worked in banking prior to marriage
-Letizia: masters in journalism. Worked in broadcast news prior to marriage
-Mathilde: completed a masters after marriage. Was a speech therapist
-Mary: degree in advertising. Worked in accounts management
-Daniel: no big education, but he did run his own personal training business
-Stephanie: masters in literature. Worked for an investment firm
-Charlene: Olympic swimmer
Heck even Camilla worked as a secretary before her first marriage. Really the only Crown Princess with a rocky resume is Mette Marit who worked as a waitress prior to her meeting Haakon.
Seems really: Love, not too many skeletons in the closet and young enough to have a few heirs are really the only requirements now a days in a wife.