Gears has a very different level of fixed characters than Chimera Squad. The latter has a small number of fixed personality squad members, with pretty narrow upgrade paths. If you need extra headcount for a mission, you can use robots, but iirc they don't get skills like the real squad members.
Gears has a couple of named characters with set personalities and physical appearances who are basically there to drive and advance the main story. You also get a fairly large number of randomly generated and fully customizable soldiers, who use the same character skills and advance just like the main characters do. Because each soldier can only go on one side mission per chapter, the randos are actually pretty important and see a lot of use. It's much closer to an RPG where you can use the pregenerated Companions with their own stories, or roll up your own party from scratch, except that in Gears you will sometimes need to use the pregens, and you have the same level of mechanical control over everybody's gear and leveling.
Also, and this is entirely a matter of taste, Gears is better written. It's kinda meat headed, but the dialog is way, way less cringe than Chimera Squad. Plus the cutscenes are in engine, and look good. Chimera Squad uses astonishingly ugly hand-animation cutscenes - I found them so badly drawn it was hard to match cutscene art to in game model. I get that the game is on a smaller budget, but I've played micro budget indices with less ugly cutscenes.