IMHO in order to understand Sulu as a commanding officer, you really have to understand George Takei and the story of his desire to want a bigger role in Star Trek.
So as TWOK was being written Takei started lobbying Bennett hard for Sulu for some kind of command position stating that (and I'm referencing his book here, don't bother reading it if you haven't it sucks) Sulu is supposed to be this brilliant Starfleet who was at the top of his class, yet after 15 years he's still just taking orders from Kirk on where to drive the Enterprise .
Whether it was meant to become a true part of the film and canon, or whether they just did it to get Takei to shut the hell up, they filmed a scene (which was ultimately cut from the film) where Kirk informs Sulu that he is going to be taking command of the Excelsior once the Enterprise's training cruise is finished (Never mind you have to be a XO for years in real life before becoming a CO, but whatever). Takei says how this delighted him at first but quickly turns sour and he blames it all on his favorite target....William Shatner.
First he said he believe that Shatner didn't put any effort into the scene and just mailed it in because the scene didn't center around Kirk. He doesn't get too specific as to what exactly Shatner did or didn't do other than to say he played it without any emotion. I haven't heard Shatner or anyone else ever give their comments on the scene so it's a one sided story Takei tells which can't be confirmed or disputed.
It seems to me though that if Shatner wasn't giving his best performance than it was up to Nick Meyer, as director, to get him to do so and say we're not calling it a wrap until I'm satisfied with this scene. Obviously Meyer thought it was good enough at some point. It remains a mystery if Meyer they got a good take, or he knew it wasn't going to be in the film so it really didn't matter and just called a day. Takei doesn't seem to know either if the scene was ever meant to be included or not.
So the scene is cut from the final film and Takei is convinced Shatner was the main reason it was taken out, although he doesn't have any real proof to back up this statement and, again, no one else that I'm aware of has backed up Takei's accusations. So you basically have a "He said.......no one else from the other side has said anything" situation.
What does seem to be clear is that having this scene cut really burns Takei's ass. I understand why someone might be upset at something like this being left out after he fought so hard to get in and it looked like he'd won, Takei though REALLY takes it to the extreme. The way he carries on about it you would think that Starfleet was a real organization and he had been cheated out of a real promotion, pay raise and command of a brand new Federation starship, instead of some fictional promotion. Or that Paramount was getting ready to spin off a new series called Star Trek: The Adventure of Captain Sulu. And it just wasn't him being on a different bridge set giving fake orders to actors that he'd lost.
Takei also doesn't seem to understand that, had he become Captain of the Excelsior at TSFS it wouldn't have made any sense at all because he would either have to:
1. Give up command almost immediately in order to help Kirk and McCoy steal the Enterprise and get to Genesis.
OR
2. Become the commanding officer and he, not Styles, would have had to been the one to try and chase down and capture the Enterprise and he would have looked like an ass when the Enterprise goes to warp and the Excelsior breaks down because Kirk and co. outsmarted him.
Also if option #2 was how it went I have no idea how he would be in TVH, I guess they could have reunited him somehow in TFF, but if he becomes commander either he can't keep it for long or he has to betray his friends, look like a jerk to the fans and possibly be written out of TVH.
Of course he is eventually given command of Excelsior in TUC and it seems that he REALLY harbored resentment since TWOK about not getting it sooner. I clearly remember him in a interview where the interviewer said how he has his own ship in this film and Takei's reply is something like "It's about time, it's long overdue and it feels GREAT" and he says it with a GREAT amount of enthusiasm and joy, much more so than you'd expect from an actor just talking about a new role.
So based on the evidence I've seen it looks like all the world like becoming a starship captain on the show was something that was VERY personal to Takei and not just about switching to a different role in the franchise.
With this in mind IMHO I think Takei decided that he was going to captain his own way. He wasn't going to be the loveable and good natured helmsman we'd known all these years. And he SURE AS HELL wasn't going to be some dramatic, free spirited but generally affable, scene eater like Shatner was. So I believe he made the conscious decision to take on the gruff, no nonsense and even a little mean at times Sulu that he became as captain.
When Jellico took command of the Enterprise-D he was a much different captain than Picard. He was curt, no nonsense and wanted to micromanage everything and didn't care about what other thought about his style and he wasn't going to be like Picard just because that's what the crew was used to. Of course this was done on purpose to give such a contrast to Picard and have conflict between him and characters like Riker.
Takei though almost seems like he decided to make himself a real life Jellico on a fictional TV series. I have no proof of this but I strongly believe that Takei, as a person not an actor, decided once we was written in as captain that he had worked long and hard to get this and he was going to do it his way and not model himself after Kirk or any other captain. If anyone involved in Star Trek, or the fans, didn't like his characterization.....tough shit.
I don't know George Takei and won't pretend to be an expert on what makes him tick. I'm just playing Sherlock Holmes and trying to deduce the unknown from the known and, from what I've heard and seen over the years, being a captain on Star Trek was a very personal thing to him. Why? no idea. Maybe it's an ego thing and he wanted to, at least on screen, be the equal of his good buddy William Shatner.
I'm not saying it's right or wrong and he certainly wouldn't be the first actor to get tempermental over what seems trivial to outsiders. I do think it seems somewhat extreme how he feels about it and wanting to bring Shatner into the whole situation, but whatever.
I just think when you see Captain Sulu on screen you're seeing what George Takei considers to be, not just a role, but his ultimate professional victory and he is going to celebrate it however he feels like it
