I disagree. Stereotypes aren't something you have, they're something that's attributed to you by other people.
For example, you might remember "that mean girl from school" but you wouldn't necessarily know that the mean girl was like that because she had really low self esteem herself.
Or you could remember that dude who always had every gadget as soon as it came out, but you may not know that it was because his parents were going through a rocky divorce, his father was filing for sole custody and wanted the boy to like him more than his mother.
The reason characters on Potters Army don't fit these stereotypes because we ask people NOT to make characters to fit a stereotype. It's quite okay if you want to your character to spread rumours or say things about other characters that imply those stereotypes, because stereotypes are shallow judgements - for example, Liesl has been spreading rumours about Alice Longbottom being a vicious firebrand - but please don't encourage people to create stereotypical characters.