There are characters which annoy other characters in the story and there are characters which annoy the audience.

Threepio in ESB may have annoyed Han Solo and Princess Leia but he was not only fun to watch but he was secretly rather heroic.

In fact it's their reluctance to listen to him that gets them into a lot of trouble.

Jar-Jar's main contribution is to remind the Queen that the other Gungans are there.

Everything else he does is accidental and moronically annoying.

The real test would be to gather sound sources and see if his dialogue could replace Jar-Jar's, be less annoying to the audience and still push the story to where it has to go.

If that can't be done there is no point trying to replace Jar-Jar with Threepio in any way.