Not really understanding the hate Isabelle is getting around the internet (or any Ultimate newcomer really). To me Isabelle is a Nintendo All-Star she DESERVED to be in this game. She is HUGE and Animal Crossing's icon! I love when Smash mixes fan favorites with "MUH RELEVANCE!" picks (sorry there is a user here I won't name but hates any character that wasn't created within the last 3 years it seems...). To me Ultimate's roster of newcomers is shaping up to be on par if not better than Brawl's IMO which to me had the PERFECT blend of newcomers. It had All-Stars/fan faves like Wario, Diddy, Wolf, Meta Knight, King Dedede added but ALSO had RELEVANCE picks like Olimar, Ike, Lucas, and Lucario (at the time obviously) added as well. Then at the same time added "Retro" picks like R.O.B and Pit. We saw that Pit went onto get a new game because of it and a lot of people view Kid Icarus as a bigger Nintendo series now than it ever was before.
Ultimate looks to be doing the EXACT same thing with all-star/fan fave characters like Ridley, Daisy, Dark Samus, Chrom, King K. Rool, and Isabelle. Except I'd argue that relevance and all-star all blend together for all these characters (except Dark Samus and K.Rool for relevance but damn sure now that he's in Smash and Nintendo has seen the overwhelming positive reception he's never NOT gonna be in another DK game again..) which is why Ultimate and Brawl IMO are looking to be the best in the series as far as newcomers go.
To me personally Wii U/3DS roster felt too much like a marketing campaign. Characters like Bayonetta, Corrin, Greninja, Robin, Lucina, Rosalina, Wii Fit Trainer (though this works as both a promo and WTF pick), Palutena (even though she is old but come on she was clearly there to promote Uprising), Dark Pit. To ME all felt like Nintendo trying to meet a sales quota instead of picking fan favorites. I get it Smash is the perfect advertising game but they went TOO overboard with it. The only "All-Stars" I felt were added to Wii U/3DS were Bowser Jr., Little Mac, and Villager. Those were the only characters I personally got excited for. Don't get me wrong or get it twisted I love when fresh new faces join the cast (like Isabelle and Inklings) but I also want fan favorite all-stars as well whether they had a recent game of not. TO me that's the fun of Smash. It's giving new series a chance to be advertised more through cross promotion but adding characters like King K.Rool, Pit, Dark Samus, Ridley, (hopefully Issac). Give these characters a second chance of life OUTSIDE of Smash Bros. I like when the roster goes evenly in both ways and not just one or the other.
Basically to sum this long ass post up. I will definitely be using Isabelle a LOT alongside K.Rool and Ridley and it's amazing seeing all these Nintendo characters together whether new or old.