Judging actor performances is of course fairly subjective but in my eyes Beltran was the worst actor on the show. He was wooden and seemed very unmotivated to me. Like Montgomery in ENT (who was kind of the opposite with his annoying uber-enthusiasm) he got his ordinary amount of character-focused episodes but later he got less and less spotlight. He played himself "out" of the show while actors like Picardo played themselves in the foreground.
You rarely know beforehand whether an actor will shine in his role. Think about Bujold, without doubt a brilliant actress. But it was the wrong role for her and they realized it before they started the show. Sometimes you only realize it while the show is running and then throwing an actor out is a fairly extreme step while giving his character less spotlight is more moderate.
But perhaps Robert Beltran would have better if they gave him better material to work with. I'm pretty sure Beltran did good work in other shows, people seemed to like him well enough in "Big Love".
Chakotay was this ex terrorist leader and the writers mainly just settled him with Native American stereotypes and cliches. I am more interested in him being an ex terrorist leader, but the writers just wanted to write as a Native American stereotype instead.
That is what I am talking about with focusing on characterization, its hard to present interesting plots when your characters are written as tried old cliches.
I agree that you need interesting characters but VOY was a John Doe show. The idea was not to show a new Klingon, a Spcok 2.0 and a Chekov-like greenhorn but to show ordinary people on an ordinary ship thrown into extraordinary circumstances. Not everybody on the ship can be an eccentric EMH or Paris.
And an interesting character can still fail. If you don't watch ENT and just read the character sketches Mayweather, the guy who is born in space, who spent most of his life on a cargo ship and unlike all the Starfleet folks knows some of what will be out there, is the most interesting one.
You can get a variety of interesting characters on a Trek show but then you have to go down the "static setting with serialization" path of DS9. People on a cargo ship or a colony or whatever are bound to be more colourful than disciplined Starfleet officers.
Again I think you are confusing normal with dull as dish water.
Riker was one of the most normal people on the Enterprise, but he was a good character overall and he got some good focus episodes. Best of Both Worlds was very much a Riker focused episode and he got a few other good focus episodes.
Was Riker the most dynamic character on TNG? No, but he was still important, I can't imagine TNG with Riker, I can easily imagine Voyager without Harry Kim.
Riker even had a character arc of sorts, going from a brass impulsive, risk taking officer to more seasoned steady officer.
Harry Kim never got such a arc, he was the green Ensign from start to finish. At one point the writers were thinking of killing him off, but only spared him after Garrett Wang was named one of the most beautiful people in the world back in 1997, that is how unimportant the character is.
Not very character has to be some uber eccentric person to be interesting, but having one dimensional cliches and one note characters doesn't create normal people, it creates bad characters.
Harry Kim never got that bad ass moment where he did something amazing and was promoted to Lt. that is an obvious way to give him a character arc and they never did it and he stayed the same one note character from start to finish. What was the point of that character when they did almost nothing with him. They could have had random gold shirts do his tasks and it wouldn't have affected the story at all.