Why do you want perches with variety? – look outside at a tree, the branches are textured and have a variety of sizes and shapes with the knots in the wood. You want to replicate this the best you can for your birds(), this keeps your bird’s feet as healthy as possible.
Dowel perches are generally avoided. That being said if your cage has one dowel perch with a variety of other perches like natural perches, it is fine to have a dowel perch in your cage too.
What is the problem with dowel perches?
The issue with dowel perches is they lack variety in diameter and texture throughout the perch they are one size and smooth. 24/7 use of a dowel perch can cause pressure sores, arthritis, and bumblefoot.
A way you can improve a dowel perch is by wrapping sections with vet wrap giving it more texture and size along the perch.
Ultimately, dowel perches are not a good choice if they are the only perch in the cage. If you only want to have one type of perch in your cage it would be best to use natural wood perches not dowel perches. If you have a wide variety of perches and your bird isn’t spending all their time on the dowel perch then dowel perches are a good perch!