There is a massive variety of female characters in Pratchett's work and they are so different I'm not even sure what you mean by that. Sure, some are bimboes or twats but I can also recall cunning, resourceful, and smart ones, and in particular the older characters such as the witches really stand out. Male characters are subject to the same amount of variety so I'm surprised at your take on gender. He does have a very stylised approach though, cartoonish in many ways and fair enough if that's not your thing.

Colour of Magic is the first Discworld, and one of Pratchett's first novels. He grew into his voice a lot more over the course of the next fifty-something novels.

Most of the strongest, most unique women I've read have been of Pratchett's creation. And not just heroes that happen to be described as female, but fully fleshed out women ranging from feminists who wish to support their husband to trans females pretending to be males dressing as women in order to fight the patriarchy.

If you're willing to give the Discworld another go, and I urge you to, there's a couple of reading order guides online. 'Guards, Guards!' is generally recommended as a good starting point, but I'd also suggest Wyrd Sisters, Mort, Going Postal, or if you really want to dive into the gender thing, Equal Rites or Monstrous Regiment.