Hey! Never Give Up, New World and Stand Up are great!
I don't think there's a single Japanese Digimon opening (and evolution) theme I don't like (I'd have to go through the Ending themes, though).
The "Digimon Fusion" theme is good, but way too Autotune heavy. Yes, we get it! "DIGITAL" Monsters, har har.
I agree Stand Up is great, but the other two I don't care as much for. Never Give Up is fine for what it's going for, but it doesn't stick with me as it feels very typical in terms of its tone and doesn't have enough to stand out from other themes like it. New World is more unique and it definitely owes that to its direction trying to fit the tone of the arc, but it also works against it as it ends up being a little too soft and somber for its own good. Both are better then the Digimon Fusion theme for the reasons you stated, but I don't think they're as memorable or even as catchy as most of the other Digimon themes around them.
Also... this.
*sigh* If only.
I have to say, they did a pretty good job with that!
Heck, even if you completely ignore the Dillon's unique moveset potential, making Dillon a sonic echo is outlandish simply due to body proportions. We're not talking a minor "few inches shorter than the base character" like Daisy or Lucina. Dillon would have to have freaky long legs, a much smaller and skinnier torso, and a completely different head shape to work as a sonic echo.
To add to this, his body proportions also come at odds with how Sonic's moveset would work. For instance, Sonic uses a lot of kicks in his movesets as moves like his Down Air, Jab 3, Ftilt, and the like all have him make full use of his long legs. Dillon's legs are short and stubby by comparison, so a lot of those moves would have to be reworked since he won't have nearly as much reach or flexiblility with them as Sonic would. You'd essentially have to put in work into a clone that by definition doesn't require as much work, and due to that it makes Dillon not that feasible as an echo .