I've never heard anyone say Darth Maul was a bad villain. If that's what you're saying, I say I disagree.
Since this is a thread about cutting out all the Sidious stuff, try doing that AND cutting Maul-- suddenly you have a movie about Anakin and Jar Jar-- Whee, that sounds like fun.
The suggestion of making Maul into General Grievous is not about saving lame characters-- it's about adding another level to two of the most memorable characters in the entire PT.
Now if this were about Making Boss Nass into Jabba the Hutt, you'd have a point.