Choice is always good when it comes to software. However, consider the following:
Point 1: Dopus5 is much, much, *much* more powerful than workbench or opus4: more powerful in almost every way. It makes using an Amiga a much nicer experience, whether you are a beginner or an advanced user. It is much better than the many utils used to prop up WB, such as deficons and suchlike. If you say you tried Dopus once and didn't like it, please try it again. It is my honest and heartfelt opinion that no-one in their right mind could prefer wb or d4 over dopus5, having used both for a long while. I think you just haven't given it a chance. You might be pleasantly surprised!
Point2: Dopus5 can be set up to look like and act like the workbench, or even opus4, if you so desire.
Point3: Dopus5 isn't bloated. It comes on one floppy disk (with an optional add-on disk). It also uses less RAM while in operation than wb3.9. It is a little slower, it must be said, than WB; but under a native PPC port, are you likely to notice?
Direct integration of dopus into OS4 would improve the Amiga user environment enormously. Giving the choice would probably make dopus as it is now - having too many patches into the OS just to work.
Think about it.