Time to go through the responses. Note I picked these basically at random
Allow me to present Lunara
Lunara is in an odd place in Warcraft lore, she is the daughter of Cenarius who was a hero unit in Warcraft 3. She is vaguely mentioned to exist ("his daughter") but there was no mention of her existence before. So she is half a new character but is derived from Warcraft lore. You may say she is a nobody, but this hasn't stopped her from popping up in almost every game I play of Heroes. People are not shying away from this character despite her being a nobody. In fact, Heroes of the Storm features over 20 Warcraft characters. So obviously that means there will be some vague and obscure characters in the mix, but this isn't stopping people from enjoying them. By focusing on a few series, the designers are able to create more interesting characters.
I'd argue that the third party characters are more boring. If you have only the biggest names, it gets dull. Smash has been interesting because you have big names and some more obscure ones. Look at say Jiggglypuff. People love her despite being an obscure choice. But by focusing so much on third party characters, you can never have a character like Jigglypuff again. It has to be the big names, and, again, its that Sakurai is scared that people will not like lesser Nintendo characters. Lunara throws this out the window. As does Valla. As does Sgt Hammer. As does Lt Moralas. The issue is Sakurai is not embracing Nintendo's lore, but Heroes is doing well because it is embracing and celebrating the lore. Blizzard doesn't care if they do something a little out there because you still have Jania, Raynor, Diablo and so on. Smash will always have Mario, Link. and Pikachu.
To close, let's look at Zelda. Folks have complained that there aren't enough characters, but that is a direct result of Sakurai being afraid of Nintendo lore. Hyrule Warriors showed that people do like these other Zelda characters. Midna and Darunia were both is titles that sold over 7 million, more than any one Fire Emblem game. So is there an issue with having them in Smash. The only issue is Sakurai not thinking folks will recognize them.
I discussed this a bit in
A Return to Form, but the series will likely have to go back. The next game will have to have cuts and there is no way that Nintendo can bring all 6 of the third party characters back. It also become more work to add more and more to these characters and fans are getting more and more frustrating with the number of guest characters. There is going back, and it makes the most sense given everything.
Major flaw with your reasoning: people are not going to buy this game for one character. If they don't like Nintendo, they will not like Smash. Also, keep in mind most everyone is here for Nintendo. I would even wager to say you are Nintendo fans.
Also, why would a Nintendo character not be fun?
Same issue: if you don't like Nintendo, you wont like Smash. I understand you and a friend got in for one character, but when you have a game with 49 Nintendo characters, you probably like Nintendo.