I have been observing this thread for a while and thought I might chip in my two cents. I still remember when I first started playing Smash - my brother had rented the original game from a local Blockbuster (that might date me a little), and we spent the next two days playing it non-stop. I was a little disappointed by the lack of villains (whenever I played games with my brother he always picked the good guys, so I developed a preference for the villains), but had enough fun as Kirby that it did not bother me too much.
I was absolutely thrilled when I learned that characters like Bowser, Ganondorf, and Mewtwo were in Melee. Over time I picked up Roy as well as a "counter" to my brother's Marth and eventually settled on Mewtwo and Roy as my mains. You can imagine that Brawl was a disappointment when I learned that both of my Smash favorites did not make the cut, but I looked at the characters and decided to give both Rob and Meta Knight a go. Eventually I settled on Wolf as my main and had a lot of fun with him.
Smash 4 was fantastic, but I was still a bit disappointed about the lack of Mewtwo. I tried my hand at Greninja and Robin before eventually settling with Shulk and Link (even got me to buy Xenoblade Chronicles to learn more about Shulk, which I enjoyed immensly).. until they announced him as the first DLC character. That was some of the best news I had ever heard!
Ultimate gave me another pleasant surprise in the form of Ridley, a character I would have loved to see but thought would never be included in Smash. I was never in doubt of buying the game, but that just got me more excited.
Where I am going with all of that is that over time I have tempered my expectations with regards to the roster. There will never be a Smash game that has every character I want to play as. I am personally thrilled as long as there are one or two characters that I love in the roster, and I am willing to get to know other characters better if there are not. I have my pipe dreams too (Neku from TWEWY, Sephiroth, Mew, Ghirahim), but I do not hold out too much hope for them and I am more than happy with the current roster.
There will always be a plethora of characters I do not really care about, but I am happy for the fans that have an opportunity to give one of their favorites a try and even though I will personally not touch some of those characters much, I look forward to facing them as opponents.
I think with regards to the roster expectation management is important with a new Smash Bros - it is very easy to fall into echo chambers on the internet and get an inflated idea of the importance or popularity of certain characters, which can lead to near certain hopes that they will be included and massive disappointment when they are not. Whether my dream roster is included or not, I can say with certainty that I have very much enjoyed every iteration of Smash and am looking forward to this new one.