I feel that both of you are correct in what you're saying!
A Fistful Of Dollars was perfect in it's execution, and the Yojimbo-story lended itself very well into a western setting. This is the film that started an entire cinematic genre!
In his subsequent films Leone always had an inclination of making the stories overlong. He also added a lot of burlesque humour to the two Dollars follow-ups. This was not entirely positive.
To me For A Few Dollars More is the least succesful of the Dollars films, it lacks real depth and has too much silly humour. Leone is just playing with all his cinematic visuals. This film feels a bit immature actually!
But it's obvious that he wanted to expand his style from the first film, and The Good, the Bad & the Ugly became near perfect, maybe just a little too long. It has a better balance between humour and seriousness. The character of Tuco is wildly over-the-top, but this is the whole point!
It's an epic adventure-film with both action, humour, drama, pathos. Someone called it a "comic nightmare of existence", and this is an apt description I think ;D