Yes I strongly believe that for the absurdity of SW to really work you always need a regular joe/sarcastic character who can step back and roll their eyes at the whole thing so that the audience doesn't have to. Nowhere is it more evident than the PT which has *no* such character. But in the OT you had Han and in RO there was K-2. Obviously Han filled that role again in TFA but in TLJ it was surprisingly Luke that had all those moments where he got to scoff *with* the audience at the narrative for the most part. Which was surprising and actually cool because I thought it helped keep his character relatable and interesting but it was also at the expense of allowing the new characters to really shine.
Which is why I really thought that Poe and Finn were even upstaged by Del Toro. "Eh, they blow you up today, you blow them up tomorrow" is one of my favorite lines in the whole movie, followed by, "It's just business." "You're wrong!" *shrugs* "Maybe." Such a great character. Poe and Finn had moments here and there but neither narrative was really "about" them enough for them to be anything more than competent supporting characters.
Del Toro's stutter drove me nuts on the second viewing.. For whatever reason I did not notice it the first time. But yeah he is better then the poorly written Poe and Finn.. That says a lot about these movies IMO..
As for the series needed a "regular/Joe" character.. Hmmmmm I was fully on board with SW well before Han ever showed up. Granted he made the film better... So I cant argue with you there.. But he is such a great character in those early movies.. I would say he toned down the "doubter" role in Empire since Luke was not around and he played everything "serious" but funny because that is who his character is.. The Humor was natural and true to his character.
No "regular/ Joe" was going to save the PT from have the issues it had.. It might have helped but it would not save it..
Regular Joes or not, I would say that the ANH, ESB, and RO just had well done humor that grew naturally from the characters. The PT had stupid humor that was forced on us with Jar Jar and the ST lacks big time in the natural humor department.. Its forced and not natural or really part of the characters.. ROTJ suffers from this a bit also.
I also don't think Han played the regular Joe so well in TFA since he believed everything by then... I also did not feel the Humor was natural for him in this film... Though I like his "that's not how the force works" line... But no look shooting and telling Chewie he likes his crossbow blaster twice was more common rule then the exception.
One of the most brilliant films to ever have natural comedy due to the "absurdity of it all" is An American Werewolf in London.. No one liners, sight gags, or slapstick... Just people behaving like they really might if such a crazy situation landed in their lap... If you are a werewolf... You just might have to deal with waking up naked at the zoo
PT and ST fail at the natural Humor aspect IMO.
I get what you are saying though.. I am just not sure its due to having a "regular Joe" character as opposed to just having better writing and humor.
Edit: Actually the more I think about it the more I may agree that the audience needed a Han "doubter" in the original.. But he did not really play that up too much if at all in the next two films.