While I believe that both versions of Johnny Bravo - those with and without Van Partible - were funny in their own ways, the ones without Van Partible are actually somewhat better, in my opinion.
After all, what are the complaints about those seasons? Johnny becoming dumber, you've got a point. The art style changed, well, I didn't mind. But those seasons turned the least-popular Cartoon Cartoon behind Dexter's Laboratory
and Cow and Chicken
into a well-remembered classic. If it weren't for the retool, it'd be on the same level as Whatever Happened to... Robot Jones?.
(It helps that a lot of the staff of the retool had worked on Pinky and the Brain
, and managed to bring that same type of comedy to the show.)
Whereas with the earlier version, there were quite a few problems - first off: the celebrity cameos. While they were often quite funny, a few of them have not aged well - anyone remember who Vendela is? It also got somewhat ridiculous in the last season to the point that Shaquille O'Neal was playing a game against Seth Green for no reason! In the retooled era, there weren't many celebrity cameos (I remember Luke Perry and Dionne Warwick, and that's it) and maybe one or two celebrities doing voices (Annie Potts in "Dude Ranch Doofus") and the show was all the better for it.
Second, the lack of a large supporting cast. Both of the other two original Cartoon Cartoons had large supporting casts. Johnny Bravo had his mother and Little Suzy...and that was that. The addition of Carl and Pops definitely helped the show, and gave more opportunities for plots.
And third, well, I preferred the retooled art style. This may be because that is the version I first saw as a kid in the early 2000s, but I still prefer Little Suzy's later design. (While she doesn't look right in the first episodes of the retool, she gets better by the third season.)
So, in summary, the show was funny throughout, but I still think the retooled version is a tad better.