I actually don't expect this new love affair with Echoes to last. I think people have generally always had issues with clones and Sakurai managed to supress that for a little while with the Echo rebranding. Post game content is different from base game, and it brings with it a new set of expectations. There's no "Everyone is Here!" to lean on like there was in base game, so echoes have to survive on their own merits in the DLC season... and I don't think they measure up on any level but towards the handful of people clamoring for them. They have very little range. Like, you list Tetra and Urbosa as options... those characters literally have no options to be an Echo of. Most of Impa's designs also don't align with Sheik's outside of Hyrule Warriors. Mrs. Pac-Man is probably never going to happen because Bandai-Namco has little to no interest in her as a character and she's missed out on any Smash representation twice now. Shadow would have also probably happened if he was possible given how he's one of the ideal choices for an Echo fighter, but he didn't. The only one you've mentioned that works is Dixie Kong, and a great deal of people prefer her to be a semi-clone and actually use her hair attacks because the whole Donkey Kong Up-B transition has always seemed like seriously underestimating the differences between what a Dixie Kong hair whip would be and DK's massive rotating his arms Up-B.
As for my issue with padding, Smash's roster is 81 character deep right now counting the existing Echoes. Smash is one of the games with the fewest number of clone fighters (at least certainly of game's this size) and it just comes off as cheap monetization when you start cranking out clones for the sake of clones. Your just throwing developmental resources to buff up a number at a certain point given how few Echoes are more broadly appealing and can contribute to Smash's legacy. Except for a couple of third party options, they largely don't and just shallowly expand universes with a different face. Again, my question is, why spend the effort developing Echoes when all of those resources could be put towards unique newcomers? If Nintendo is only giving a shoestring budget to support Ultimate, sure, they make sense in that scenario, but that's completely unlikely to be the case given what has been said about the next wave already and how they're all in on post Fighter's Pass support. People on average prefer unique newcomers (look at every poll, it's dominated by characters that would have to be unique inclusions), so in the name of accomplishing your goals as a developer, I don't see the logic behind continuing Echo fighters.
Will they sell? Yes, of course they will. But it's the same argument as first parties vs third parties, except, as I've mentioned before, the issues of the first parties are exacerbated. All of these options will sell in a vacuum and appeal to specific audiences, but which ones are the most beneficial from a sales perspective, which ones benefit the ongoing health of post launch support the most widely, which of the options satisfy the fan base, etc. Nintendo is a company we all like and even love, but we would do well to not forget that they are a business looking at their business interests and Smash is a cash cow that they are looking to make the most of and Sakurai is looking to passionately expand Smash in meaningful ways. I just don't see them aligning with those goals in the same way as others.
