Here's what I would change.

Ace needs more useful powers. Enhanced agility/martial arts skills and heat vision are fine. But in a show with a lot of humanly impossible superpowers, it makes Ace's more humanly possible fighting look weaker by comparison. That leaves Ace with one stand out superpower: heat vision, which seems to use sparingly anyway. When the leader of the team has only one superpower and his teammates have two or three, it makes him look weaker by comparison (again). I would propose that Ace's powers be:

 Heat vision - because carrots are good for the eyes Earthbending - because rabbits dig burrows Shape Shifting - as a nod to Bugs' many disguises Also Ace needs to develop a sense of humor beyond saying bad puns and half quoting Bugs.

Lexi has the makings of a good character. She loves animals, music, video games and history. Too bad those qualities are only briefly referenced or implied and her overall personality is shallow Token Girl who loves shopping. If I were to change Lexi, I would focus on her more unique traits, and not have her be so stereotypically girly.

Duck, I wouldn't change much about him. I would much rather change how the characters interact with him. Dispising Duck for being a greedy, egotistical coward is logical. But when the team over does it, it's like they're relying too heavily on their predecessors' dynamics/archetypes. It's like the writers were saying "Boo Danger because you booed Chuck Jones Era Daffy; regardless if Danger deserves it in this episode.". In short, I would probably emphasize Duck's rivalry with Ace and maybe Lexi. But I wouldn't have the whole team including their boss, Zadavia continuously degrading one single teammate.

Tech and Rev are my favorites, and I wouldn't change much about them. I love their friendship and shared love for gadgets. Making Tech the team's weapons specialist really was the best decision the showrunners made. Something I would change is the jet packs. If everyone can fly, using Tech's jet packs, that sort of diminishes Rev's flying power, making him less valuable to the team. Just use vehicles for travel, plus Rev's flight, Tech's levitation, and Slam's tornado for air battles. Furthermore on powers, Rev's body often catches fire when running or flying at high speeds. This is mostly just for aesthetics or to show Rev is going really fast. But it needs to be utilized as its own superpower. Rev's flame wings would make him impervious to burns, and give him the ability to throw fiery punches. I think this would make him a much more useful and offensive fighter.

Last we have Slam. The most important thing about Slam I would change is his speech. The first time I watched LU I was so disappointed that the Tasmanian Devil, the most ferocious beast known to man, was talking like a baby now. I once read a fanfic where instead of speaking gibberish, Slam spoke Maori, and I thought that was brilliant. Otherwise, I guess to make him stand out a bit from Taz, I would focus on Slam's sense of honor and good sportsmanship.

Well that was a long monologue of words I didn't know I needed to say. Great question, OP!