Well sparing the ethics behind it, I can't possibly see how you think that hacked characters can be indistinguishable. Truthfully I don't know all that much about the more advanced ones, and thus I would like to request a good example of what you think has the most quality, but from the odd few that I do see here and there, they are pretty sloppily intergrated, and certainly noticable. For one, mostly every new character I've seen has moves taken from other characters, and if the model was actually imported from another game, its garishly obvious that it should be there in Smash. Then again, with all the hacked in music and stage textures, I guess it may seem just as at home as anything else in what has essnetially boiled down to MUGEN 2.0.
But as I said, I don't pay all that much attention to the hacking scene, so if there really is some quality work coming from it, I'd really be interested to know.
Which ones have I been impressed with? My short list:
BigSharkZ's Mewtwo
Eldiran's Zero
Shadic's Geno
Akari Un's Cloud
Keep in mind that I've been following the PSA scene closely ever since Phatomwings released
Phoenix Mario, the first PSA, last summer. As you can see, things have come a pretty long way since last year. Are the characters still kind of gritty? Yes but you have to keep in mind that they're not being made by professionals. They're not perfect by any means but give it a couple of more years and I'm sure there will be stuff that will rival what was originally put in the game. Also, I never said they were indistinguishable now but I believe they have the potential to become that way eventually.
I believe Toise said it best a while back, "It's not so much the series of origin that is important for a character than it is the character itself."Obviously not verbatim, but the point still stands.
Come to think of it though, I would like to know what the priorities are for some of these inclusions. I believe the lack of Dedede and MK was due to Sakurai trying to be modest (some would say otherwise in Brawl), and that they were included in Brawl partially because Brawl could have very well been the last time to work with those characters again since he was still freelancing at the time.
I'm guessing others such as Wario and Diddy were excluded from Melee because of time considering they only had somewhere around a year and a half to work on it. If we exclude the clones, the newcomers were Bowser, Peach, Zelda, Sheik, Ice Climbers, Marth, Mewtwo, and Mr. Game and Watch, only nine newcomers before the decision to add clones (maybe).
An explanation for the first three (and arguably Sheik) aren't really needed. Ice Climbers was the chosen retro character, Marth I'm not sure of (can't complain though), Mewtwo is just Mewtwo, and Mr. Game and Watch was, IIRC, a tribute to Gunpei Yokoi.
In the case of Young Link and Ganondorf, those two were clones (should've been better handled in Brawl, IMO) of pre-existing characters thus explaining their inclusion in Melee. Everyone else was more or less, "Meh, we can do it."
Sorry, but I'm just rambling here.
I've shown this several times before in the past but most of the new characters that appeared in Melee (Bowser, Peach, Zelda, Young Link, Ganondorf, Sheik, Marth, Falco, and Mewtwo) did very well in the Melee poll and ranked high in their respective categories. Pichu represented the most recent Pokemon generation, Roy represented the most recent Fire Emblem game, the Ice Climbers were retro and appeared on the poll too, and Mr. Game and Watch kind of came out of left field. Dr. Mario, from what's been said, was the only character that was added simply because "he felt like it."
With Brawl, I believe a lot of the characters selected strongly correlated to the Melee poll and were essentially "left overs." Wario, Pokemon Trainer, Diddy, King Dedede, Metaknight, Wolf, Pit, and Sonic appeared on the Melee poll and all except Wolf and Pit had a large number of votes towards them (usually ranking just below the characters that actually made it into Melee). Snake was a supposed Melee leftover because Kojima approached Sakurai too late about Snake's inclusion during Melee's development. Lucario represented the most recent pokemon generation, Ike represented the most recent Fire Emblem game, Lucas was originally planned to replace Ness in Melee but Sakurai got cold feet, Olimar represented the only major Miyamoto franchise that wasn't represented by someone at the time, ZSS was an extension of Samus, and ROB came out of left field.
There's a lot of other stuff that he's explained for a good number of characters (for example, Ganondorf wouldn't have even added to Melee if his body type wasn't so similar to Captain Falcon) but I just wanted to leave this as food for thought.